We do have two complete manuscripts, Codex Oblongus and Codex Quadratus, as well as the partial Gottorpienses -- all Carolingian and from the 800's.
Speaking of the Carolingian period, I recently learned how the Muslim scholars had translated a great deal of Greek writings into Latin (many who lived in Islamic Spain). I wonder why, other than that they abhorred Epicurean denial of life after death, they didn't translate Epicurus, too. Perhaps all of the loss occurred before the 800's to 1000 CE period. Anyway, it is a question that likely can't be answered