Elli Thanks for calling my attention to the work by W. Kendrick Pritchett. I'll definitely take a look at their work and post thoughts over the next day or so.
Are the two of you together?
No, we definitely have differences of opinion, but I'm more than happy to go back and dig into the research. 
Just currently involved in other commitments, so it'll be a little while before I can post again.
I have become convinced by @Don's argument and I believe that disputing it will require (at least) adequate answers to questions that arise from the position that Diogenes provides inconsistent dates that require explaining:
1. Why would Epicurus choose to celebrate his own Birthday on a day that is other than his birthdate?
2. Why would Epicurus appropriate practices from the pre-existing cult of the Eikadistai who celebrated the 20th?
3. What justifiable significance would be attached to the 10th compared with the 20th (or 7th)?
4. What significance would the 10th and 20th carry for someone born on the 7th?
5. Given that later biographers of Epicurus did not use the Attic calendar, why would they have felt it more important to denote the day within Gamelion rather than explaining to their readers which sequential month is Gamelion?
From the book Elli referenced in her post above:
Athenian calendars and ekklesias by Pritchett, W. Kendrick (William Kendrick). 2001
Accessible to borrow for free at Internet Archive https://archive.org/details/atheni…ge/n14/mode/1up
The chart on p. xiii:
From Pritchett's note on p. 56:
Pritchett also has a book on the Choiseul Marble, also available to borrow at Archive:
From that book, here is the footnote on p. 24
In light of Pritchett's critique of Meritt and his Choiseul Marble text, I may substitute Pritchett's work for Meritt's in my paper. However, from what I read in Pritchett's books, the basic thesis of the "earlier tenth/προτερα δεκατη" = 20th of the month still stands from my perspective.Pritchett does talk a lot about the omitted days that determined the hollow and full month, but the term for the 20th appears to stay intact. If someone checks out the book from Internet Archive, please feel free to correct me if I'm reading it wrong, please!
Pritchett also praises Chronologie Untersuchungen über das Kalenderwesen d. Griechen, insonderheit d. Athener
by Mommsen, August (1883) available for free (but in German!!) at Internet Archive as "the best collection of days in literary resources." In fact, Mommsen seems to be skeptical of the use of προτερα δεκατη; however, he also seems to assert that Epicurus's Will should be interpreted as Epicurus referring to both dates as the 20th within that section of his Will. If Martin would weigh in the German when he has a chance, it would be greatly appreciated. I'll put it below. That said, it appears Pritchett is fine with asserting "δεκατη προτερα = 20th" later and in the note in the Choiseul Marble. Mommsen did publish his work in 1883. Kendrick published in 1970, so I'm not sure Mommsen had access to the Choiseul Marble.
Mommsen, pp.93-94:
I mean this humorously and I am in no way turned off by the discussion as I find it fascinating but what's the sentence in the raw material that stands out?
"Discussion of the details of the Athenian calendar became in their hands so abstruse that for decades few other scholars have ventured into the jungle."
I have no opinions on this but reading about these details is fascinating.
At first sight, Mommsen points out inconsistencies/problems with the reconstruction of the meaning but does not come to a conclusion within the German/Greek text quoted in #103.
By the way, August Mommsen is an example of cutting-edge research carried out by high school teachers in Germany around the 19th century. Georg Ohm is maybe the most famous example. He experimentally showed the law which was later named after him.
At that time, at least some teachers at high schools in Germany were called professor.
I mean this humorously and I am in no way turned off by the discussion as I find it fascinating but what's the sentence in the raw material that stands out?
"Discussion of the details of the Athenian calendar became in their hands so abstruse that for decades few other scholars have ventured into the jungle."
I have no opinions on this but reading about these details is fascinating.
Oh, and we're not even discussing the "abstruse" part!! 
If you take a look at their books in Internet Archive, you'll see abstruse! Calculations of days correlated with lunar cycles cross-referenced with prytanies and archonships with discussions of omitted days! By Zeus, the Athenian calendar was definitely a constant work in progress and it looks like it was overtly political and open to revision when it came to something as basic as the number of days in each month!!!
Hello to all epicurean friends,
I was late to answer at this thread and on the issue, as has been studied and written by our friend Don , and discussed with the rest of us, because I had a private communication with a greek person named Orestis Pylarinos who keeps everyday and with responsibility the ancient Athenian Calendar with the customs and celebrations of ancient greeks.
Orestis Pylarinos is a mathematician, he speaks both the greek and english language, as he has studied in the US at UCLA Mathematics. In our communication, Orestis Pylarinos said to me, that he would have no problem joining this discussion as it evolves, concerning which is the right date to celebrate the birthday of Epicurus. 
Cassius , my friend, please inform me if it would be ok with you to announce him this website forum and his participation to it. And IF yes, please give me some instructions and info.
Thanks.
P.S. 1. Orestis Pylarinos profile at FB in which he announces in public, the ancient Athenian Calendar is at this link. We read at this link that he refers to Epicurus birthday.
(https://www.facebook.com/SacredAthenian…aK7BFZV1gj8Zt2l)
2. And the website with the ancient Athenian Calendar is at this link:
athenianyear.wordpress.com
Elli that would be great! Please tell him to visit this link:
When he does he will see the REGISTER button on the right side of the screen (or the top if he is on a telephone)
At present we let everyone register regardless of their personal philosophy, and if you will just ask him to identify himself in a post as being your friend, we will make sure that he is well taken care of.
Thank you and let me know if I need to do more to help get him in!
Οk my friend Cassius. I've point out to him the website with this forum and this link.
Goodnight! 
I just clicked through to
That's quite a website!
I'll be curious to see where he got his information on the names of the days.
It appears to meet that his calculations are the same as the calendar at
I found last night that Hesychius of Alexandria in his Lexicon of unusual and obscure Greek words written in the 5th or 6th c. CE includes the following entry:
δεκάτη προτέρα· ἡ πρὸ εἰκάδος, ὡς ὑστέρα· ἡ μετ' εἰκάδα
δεκάτη προτέρα· ἡ πρὸ εἰκάδος ("for/instead of εἰκάδος/20th"), like ὑστέρα· ἡ μετ' εἰκάδα ("after εἰκάδα/20th, i.e., 21st")
PS: Note - I'm getting that use of πρὸ from LSJ, definition III.1.
Henry George Liddell, Robert Scott, A Greek-English Lexicon, πρό
III. in other relations:
1. of Preference, before, rather than, κέρδος αἰνῆσαι π. δίκας to praise sleight before right, Pi.P.4.140, cf. Pl.R.361e; πᾶν δὴ βουλόμενοι σφίσι εἶναι π. τῆς παρεούσης λύπης anything before, rather than, their actual trouble, Hdt.7.152 (so, in order to avoid, “π. τοῦ δεινοτάτου” D.54.19); “πᾶν π. τοῦ δουλεῦσαι ἐπεξελθεῖν” Th.5.100, cf.4.59; ἑλέσθαι, αἱρεῖσθαι, or κρῖναί τι π. τινός to choose one before another, Id.5.36, Pl.R.366b, Phlb.57e; π. πολλοῦ ποιήσασθαι to esteem above much, i.e. very highly, Isoc.5.138; “π. πολλῶν χρημάτων τιμήσασθαί τι” Th.1.33, cf.6.10; π. ἄλλων more than others, Pl.Mx.249e (v.l.), cf. A. Th.1002; δυσδαίμων . . π. πασᾶν γυναικῶν ib.927 (codd., lyr.); “π. πάντων θεῶν τῇ Ἑστίᾳ πρώτῃ προθύειν” Pl.Cra. 401d: after a Comp. it is redundant, “ἡ τυραννὶς π. ἐλευθερίης ἀσπαστότερον” Hdt.1.62, cf.6.12, Pl.Ap.28d, Cri.54b, Phd.99a; for ἤ after “ἄλλος, οὐδεὶς ἄλλος π. σεῦ” Hdt.3.85, cf.7.3.
That's an ancient author providing specific definitions for both δεκάτη προτέρα and δεκάτη ὑστέρα as alternative names for the 20th and 21st days of the month.
Hesychius was probably not a Christian. Explanations of words from Gregory Nazianzus and other Christian writers (glossae sacrae) are later interpolations
I wonder if Epicurean possibly, or Stoic.....
I wonder if Epicurean possibly, or Stoic.....
My guess would be Aristotelian because he obviously liked to make long lists of things 
From my perspective, this is big. I just found this in Pliny 's Natural History, 35.2:
Thus it is that we possess the portraits of no living individuals, and leave behind us the pictures of our wealth, not of our persons.
And yet the very same persons adorn the palæstra and the anointing-room4 with portraits of athletes, and both hang up in their chamber and carry about them a likeness of Epicurus.5 On the twentieth day of each moon they celebrate his birthday6 by a sacrifice, and keep his festival. known as the "Icas,"7 every month: and these too, people who wish to live without being known!8 So it is, most assuredly, our indolence has lost sight of the arts, and since our minds are destitute of any characteristic features, those of our bodies are neglected also.
The footnote - from John Bostock in 1855! - says "6 In reality, his birth-day was not on the twentieth day of any month; but, for some reason which is not known, he fixed upon this day.—B. He was born on the seventh day of the month Gamelion."
LOL!! Although later parts were published posthumously by Pliny the Younger shortly after Pliny's death during the destruction of Pompeii, Pliny's Natural History is from the 1st century CE **when there were still practicing Epicureans right in Herculaneum near where Pliny actually had a villa!!!*** Pliny no doubt knew Epicureans first-hand!! For me, I'm going to take the word of Pliny over a 19th century scholar!
In Latin:
iidem palaestras athletarum imaginibus et ceromata sua exornant, epicuri voltus per cubicula gestant ac circumferunt secum. natali eius sacrificant, feriasque omni mense vicesima luna custodiunt, quas icadas vocant, ii maxime, qui se ne viventes quidem nosci volunt. ita est profecto: artes desidia perdidit, et quoniam animorum imagines non sunt, negleguntur etiam corporum.
Very interesting and a great point that applies often when we think we understand Epicurus better than did his ancient followers!
Also Don what do you take Pliny's point to be in this discussion? The "thus?"
Also Don what do you take Pliny's point to be in this discussion? The "thus?"
We don't live on after we die. The portraits (to which he was referring in the previous section) simply display the wealth of the dead people, not their character.
And this is important for the 20th discussion because Pliny was not Epicurean but he reported what he saw and what he was told. The fact that his villa was close enough to Pompeii and Herculaneum that he could get to the doomed city while the eruption was happening tells me he undoubtedly had contact with Epicureans. He didn't celebrate the Eikas but he could have easily seen people celebrating it. Same goes for Pliny the Younger of someone wants to say that her added this to book 35. Either way, we're covered!
I checked, and Pliny was staying for some time in Misenum (modern Miseno) with his sister and nephew (Pliny the Younger) and was there when Vesuvius erupted. That's literally only a 7-8 hour *walk* from Herculaneum (modern Ercolano), arguably one *the* hotspots of Epicurean activity in ancient Rome. So, yeah, Pliny easily saw, talked to, and had first-hand knowledge of Epicureans while writing his Natural History.
