I've never heard of one with an enclosed hammer. I have seen the shortened "police" version which is shorter than the military version and even a target version. One of the local shops has one marked "9.3mm" but no enclosed hammer. I used to have a good Nagant site bookmarked but have no idea what happened to it. I'll see if I can find it and post back.
IIRC the Polish also manufactured Nagants and maybe Spain(?) in addition to the Belgians and Russians. Since the bullet is actually 7.49mm in diameter then maybe that's what the barrel marking is.
If you find info on another site, please, post it here. I am really curious!