In 2015 I said that I think the overprints are from typographic plates but carefully applied so that there is not always show through at the back. This claim is supported now by the block of 50 kop shown below. It's from the top left corner of the sheet and if you look at position 1, you can see that there is a slipped cliche - a cliche out of line. This is not always present as is shown from the block of four 1 kop also from the top left corner. So this suggests fairly definitely a typographic plate and the slipped cliche would explain the occasional single copies of Kherson tridents which look as if they are from a handstamp, carelessly applied:
I found I had only one expertised copy of a Kherson Trident, the stamp below which is signed Dr Seichter and which could be used for reference. But the one kopeck block above also provides essential information.