1727 Russian Polushka - How To Authenticate?

Russian coins are mostly right out of my wheel house, especially anything this old.

I've had a fairly quick look around to try and figure out how to confirm this is a copy. I see quite a lot of variety among the copies, and nothing seems to align with this. And neither do the real ones. I know there will be variety among fakes, but is there variation in the genuine ones?

I've had this and a number of other 18th century Russian pieces for at least a decade, but I don't know where they are this moment, so this is as good as it gets in terms of photos for now.

Yes, verdigris sucks.

Thanks.