When if ever were scope rails installed on polish AKM47military issue rifles?

Polish AKMs have been retrofitted as well as specifically produced with optic rails.  The first known production model with rail was in 1977,  however, like I said many rifles even earlier than this date were retrofitted.  Known batch codes for these models include AN, NO, CH, ZC, and PC, and as you can see from the code variations they were intermittent in the production line.

Here is a pic of the different rails the Poles used AKML/AKMS-N up to the Tantal...



Here is a pic of a clone of a Polish AKML with NSP-3