Keykeeper.
To your first question, Yes some do have a flat back (handle side), one drawing in a sheet metal book (Atkins 1927) even shows the angle pein opposite ways each end. Some makers just used the riveting hammer forging for the paneing hammer (to save tooling?) and just ground a sharp angle on it.
The cat.. page is certainly not very clear, but I think you'll find that normaly the riveting hammers had a 1/16-3/32 radius and the setting/paneing hammer was a sharp angle. Regarding categorizing and naming, I think there was/is a disconect between maker and user,which is growing as the years pass, the two processes we are talking about (wiring and riveting) aren't done commercially any more but are more in the relm of hobbiests.
Isn't part of the challenge and (fun?) of finding and identifying old tools trying to sort out the wood from the trees!
Graeme
corrected a statement (the Stanley Atha paneing hammer does have a flat back)