Sonny,
40+ years ago is when they were first made.
I seen a picture of one about 2 years ago and that was all I needed to built it.
Since then I have seen some on videos, but I have not seen anyone stacking the bales and then picking up the stack.
I am going to make a QA for my 3 pt, so I can move 64 bales at one time to the barn.
Load one and unhook, load another one and then pickup the first one with the 3 pt.
You can go to Cabin Hollow Metal Art on FB to see a video of it working.