Indeed, there were plenty of issues with the mints, as they could never mint coins into proper circles, or actually had enough silver planchets to start off with. While it was quite common in Peter II coinages to use foreign European silver coins to overstrike on, it is not clear if this practise still continued into Anna's era, although copper overstrikes of Peter I still occured till 1735.
Here is my example, but is not a typical average Anna ruble:

Usually, if you notice the bust of Anna, it should be a cross, instead of a scarf.
Edge:

This is the very first time when such coin edging technology was seriously considered to counter people scrapping silver off from edges in massive scales. Unfortunately, this only lasted till 1743, when the mints decide to revert back to the extrusive text, as they probably thought that it is a waste of space.


