Teachers of Ancient Greek at my university have always been emphasising the importance of being aware of the loss of the intervocalic sigma in the language's history, because it helped to understand some seemingly peculiar inflectional paradigms ( τὸ γένος etc.). Unfortunately they were mostly literature specialist, not linguists, so they only provided us with the most essential information.
What about the dating of that sound change ?Was it during the Proto-Greek period ? Can we find that change in all the dialects ?
Also, what the about the forms that actually have an intervocalic sigma? Such as φύσις, βάσις, στάσις etc. or the sigmatic aorist like ἐτιμήσα, ἐπαιδεύσα. While I can understand the nouns as a post-change creation, this aorist seems quite ancient to me, but I very likely might be wrong here.