Bulgarian coins dated 1951

[java_lt]

Hello everyone,
who could help me - Bulgaria 1951 dated coins were struck in Leningrad Mint (USSR) and Sofia Mint (Bulgaria).
Is it possible to distinguish where the Mint has been minting coins ?
How and where to find the differences ?

java_lt

[Siberian Man]

No. All of these coins has no mint mark.

[Siberian Man]

And one coin yet.

[Globetrotter]

I found an image in numista with the mint of Leningrad and a small explanation, this only for the 1 stotinka, maybe it's valid for the rest of the 1951 coins as well?