Welcome back, Charlie. Links that might help you get up to speed:
OOTP19 features:
https://forums.ootpdevelopments.com/...d.php?t=285737
OOTP20 features:
https://forums.ootpdevelopments.com/...d.php?t=299260
OOTP21 features:
https://www.ootpdevelopments.com/newsletters/nl0270/
Major announcement:
https://forums.ootpdevelopments.com/...d.php?t=321116
Were you still around when historical minor leagues were added, and Negro leagues? Historical injuries were added to the transactions file. I'm sure there were some other small additions.