V10R1 - Compatibility with the behavior of Db2 11 new-function mode. After migration to Db2 12, this value has the same result as specifying V12R1M100. (https://www.ibm.com/docs/en/db2-for-zos/11?topic=11-db2-migration-modes see bottom of page)
V11R1 - Compatibility with the behavior of Db2 11 new-function mode. After migration to Db2 12, this value has the same result as specifying V12R1M100.

V12R1M*** (stars = function level detailed here https://www.ibm.com/docs/en/db2-for-zos/12?topic=12-db2-function-levels)

So in the context of DB2 v12, seems V11R1 is equal to the lowest DB2 12 function level (V12R1M100), which has parity with V11. Then levels 100, 500, 501, etc add more functionality each.