Cool stuff!
I'm wondering where those roster limits come from. In the milbleagues.csv file, which would
seem to be a likely source, there are fields for active roster and reserve roster limits. However, those don't jibe with the limits you reported. For example, here are the the active & reserve limits for 1919, 1920, 1921, and 1922, per that file:
1919 - Texas League: 15, 11
1920 - Tx Lg: 15, 11
1920 - Negro Lg: 20, 13
1921 - PCL: 25, 10
1921 - Tx Lg: 20, 10
1921 - Ng Lg: 20, 10
1922 - PCL, Tx Lg, Ng Lg: same limits as '21
In addition, if you create a game starting with the 1920 season, OOTP does not reference this file; it pulls its league & structure data from its "game creation program" (for lack of a better term). It only uses this file (and others) for subsequent seasons... That said, the data in the game creation program
should match what's in the csv file...
Overall, a bit of mystery, though...