Many of these can be seen in the Anne S. K. Brown Collection at Brown University, RI.
In the collection it appeared to me to be a few different series. There were duplicates, some plates colored, some still black and white. I think there were no non-Guard units. It's my sense that these had semi-official status. I also strongly suspect that Viskovatov's big project used these as partial inspiration. I wonder if some of the artists worked both on these prints and under Viskovatov.
I think the only way out is to examine everything for artist's names and publishers. Viskovatov's engravers had their names on each plate.
All these far surpass Eckart in detail, so there is no question that they precede that series.
Sorry I don't have answers, just free speculation.