A show like Adventure Time took us Eight seasons to find out any shit about where Finn came from, im not really in any hurry. With only one season left things are probably gonna be left to a Lore book.

Centipeedle's testimony probably wasnt anything other than her life story during the war. "I fought, I got lost, I turned into a monster, Diamonds did it". The gems already knew what corrupted gems were, maybe even already have an idea of 'what' changed them. Ergo centipeedle's story is more for our benefit than theirs.

And really it doesnt matter how much information gathering the gems do on PAST gem society, as Lapis said, everything advanced beyond, there is now an entire SECOND era worth of gem advancement. Peridot's a kindergardener, so she barely knows anything useful to war other than the soldier built in the past. Lapis was there but she couldnt make heads or tails of anything.

These are just my ideas on things, there is a chance of them being addressed in season five, or in an after series lorebook. But not every show neatly wraps up its plot threads, and some are left even after its end. Its just getting there to see what is eventually left in the shows wake.