Interesting question Oscar, but I think it has less to do with whether something is "fixed or unfixed" as it is instead the variety of the sources that we gather from. As you have probably surmised from the thread discussing the SoFE's 20 tenants, there is of course the classical interpretation, or in other words what Epicurus had envisioned, to understand his words in the context of Ancient Athens (ie why the problem of evil makes little sense when attributed to Epicurus). Indeed Epicurus himself told his students that they should write their own outlines and understandings of the philosophy. It's written in the Letter to Herodotus:
"Those who have made some advance in the survey of the entire system ought to fix in their minds under the principal headings an elementary outline of the whole treatment of the subject. For a comprehensive view is often required, the details but seldom. ... For it is impossible to gather up the results of continuous diligent study of the entirety of things unless we can embrace in short formulas and hold in mind all that might have been accurately expressed even to the minutest detail."
However, given the history of the philosophy, it most definitely grew within the following centuries after his death, we see this with Lucretius and the elaboration of the idea of the Atomic Swerve (Clinamen), or throughout the middle ages up to the Enlightenment when EP was beginning to have the proper recognition it so rightfully needed when Lucretius and Epicurus were invoked alongside the materialists and hedonists and became incorporated into sophisticated worldviews. Simultaneously, even, the works of the Epicureans began having a clarity or revival so that they could be studied and accepted on their own merit without the help of Enlightenment thinkers using bits and pieces.
Epicurus himself was wise and proficient in philosophy, that we do not deny, but having a fixed view of him isn't too unlike an "ideal" Epicurus where we conveniently forget his statement about the sun or his meteorological predictions in his Letter to Pythocles.
Epicurean Philosophy stands as one of the few surviving ancient schools of thought, and almost alone in actually being right and correct without revisionism.