Just stumbled on this. Not sure if it includes all 18 volumes of plates but there a good many. First published in the late 19th Century, Uniformenkunde is one of the most important secondary sources of uniform information. The original sources Knotel used are not always clear and there are some errors but it is a wonderful resource nevertheless.
A lot of nitpickers and purists knock Knotel for as you say, lack of clarity in sources, and some believe a few to be made up. But that sort of thinking is overkill to me and I consider it a great resource.