Some enthusiasts brought stamps of the Romanov and the charity set to Armenia and had them overprinted. Later forgers discovered that they like these stamps too. They are bigger and just look like more. Nowadays collectors often think likewise. Still, most of the overprinted stamps on the market bear faked overprints.
Here two lots that carry faked overprints.
Yes, most overprints on Romanovs and War Charities are fakes, sometimes stupid ones: the first stamp you illustrate (3r on 3 kop) has a St Petersburg postmark. If you don’t know that St Petersburg is not in Armenia, maybe you shouldn’t be selling Armenian stamps 🙂
I think some supplies of these stamps were still in Armenian post offices in 1920. You can find large multiples of the 4 kop Romanov and 10 / 7 Romanov with genuine overprints, and this suggests to me that they were in the post office cupboards. Other values, I am not so sure.