I know that you are a very experienced and reputable collector, so I would like to mention that the only thing, that made me suspicious too, was the serial number indeed. The "1" should have an underscore beyond it and the "2" misses the little "hook" at it`s right end... I will see, if I can get better images though.
Some pictures of the Navy Order Admiral Nakhimov. Numbered # 2653, but the nummering looks to large and the medal seems to have a hallmark on the top. Was it usual to hallmark these medals and using too large letter types?
Thanks for your help.