To me the ones shown look totally false and too blingyfied. Artistic licence I suppose.
When I used to study old engines, they were just a flat plate with the top and bottom of the corners chamfered to stop them digging in, with a hole thru them. The only time I saw any that were like the ones shown were when they were used mainly for decoration. A lot of the time they weren't even square, but sort of parallelogram shaped. They were just cut from strip metal, most probably with a cold chisel.
It wasn't until Joey Whitworth came along in the 1840's and standardised screw threading did you get any sort of semblance of a standard and things were made to all look and act the same. Before that, they were usually being hand made, with the nut being made to fit the thread on the bolt, individually, and so things didn't look so regimented.
I personally reckon Gerhards model would have been from that 'hand made' sort of era, not the regimented way the later Victorians did it.
If you are still having trouble Gerhard, email me a sketch with the dimensions you require, and what material you want them out of, and I can easily knock out a few dozen flat plate nuts for you. I have all the correct holding gear to cater with square section. But you will need to do all the deburring yourself, they will just be parted off at the correct thickness you will most probably have to run a tap thru them again as well, just to clean up the threads after parting off.
Bogs