I could not stop wandering about all of this, so I called Izhmash directly today.
All Saiga 7.62 x 39 models could have a stepped chamber. Apparently, they use whatever is in stock at the moment of assembly.
Models that are meant for export are not checked for this gun control measure. Well, that confirms the suspicions.
I asked if it was possible to order a model that would accept standard AK magazines, but the answer was no.
On the other hand, it is possible to get a non-stepped one. The lady could not tell on the phone if that would mean any extra costs, though.
It’s also not