Hi
So many questions in your post, nevertheless you raise many interesting topics!
I'm too tired to make a constructive answer, so here are some random facts:
1/ like in every other versions of NBA Live, overall ratings are pretty much fucked up. They can give you an indication if the player is a superstar, a starter or a role player, but don't give it too much importance. In general, Live 2000 tends to overate PF and C, while SG and PG are underated
2/ you're talking of a "recent roster update", are you talking of mine? If yes, well, overall ratings are fucked up. I have to update ratings with an external editor because if you update ratings in the game, it will automatically fuck up the salary value. So with an external editor, overall ratings are no longer updated... I update it manually, but it does not necesarily reflect what the game would give, all the more as I try to compensate the overated PF/C problem
3/ players stats are also calculated with DSTATS values.
Check also this page, you may learn interesting things