Just wondering - how common were they?

It must be quite scarce as they rarely appear under overstruck dengas (1730-5). I believe I have 4 samples overstruck, 3 to be 1731, the last one likely to be 31 as well, and Steve holding a 1734 example. There is one highly suspicious one that seems to be overstruck but this is dated 1753 and has the date 1724 barely on it, so it does not make ANY sense!

This one....
Click to view attachment
1734 Denga struck over Rare 1724 Kopeck.

Reverse
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Steve, if I did the overlap right, this is how it looks like:





Makes me feel that I'm reviving a ghost back alive...

There was a very nice 1724 kopek in World-Wide Coins auction two days ago. I am pretty sure it sold for 50K +.

Very nice! Great job!

Looks like I'll have to stick with overstrikes

Here is the questionable 1753 denga that I have. The letter "O" is at the right side of the wing (the location of the word kopek might be 160 degrees clockwise)



You can see a bare faint line of a rectangle box which usually leads to the identification of the 1724 kopek. That's how I positively identified the others but this is more of a challenge. Sometimes looking at an overstruck coin makes you feel totally hallucinating...