I'm a bit late to this but just to add my twopennorth - I'm as sure as I can be that there are originals with no stamp, as others above have said.
I base this on a few things but mostly that I got my copy from a tiny little record shop in York, Pennsylvania, in 1988 (I actually got three copies and sold two, one to Danny Everard I *think* though that might be wrong, it's a long time ago) - all marked with the same 'play side' felt tip cross as in one post above.
I am aware of the pressing situation in the States - it's obviously where a lot of boots were made, and indeed I have visited pressing plants in search of info and maybe even tapes etc back when it was worth going over (never got much useful info or tapes mind you!) - but it beggars belief to me that anyone would go to the trouble of producing an Eddie Parker boot (or any boot) and then ship multiple copies to insignificant record shops in outlying northern towns where they could possibly be discovered and bought for 50c each years later. It would cost more to produce and ship them.
I can understand why it would be worth shipping to someone like Val Shiveley (not imputing anything improper to Val), because visiting his place in Philly was like walking into Hurts Yard some days - more Midlands/Yorkshire/Lancashire/Sweaty accents than local.
If Val had wanted to, if the boots had been really good, and if he'd been prepared to do it, he could easily have knocked out boots to unknowing northern punters, certainly back in the lower-information pre-internet days (not that he would.) The very fact that it came from Val Shively (or similar) would have given it the necessary imprimatur.
But a little mom and pop operation run by a bloke who also sold toasters and CB radios five hundred miles from Detroit? I don't think so. Makes no possible sense.
It is easy to identify some known bootlegs but hard to prove a negative, given the chaotic and fly-by-night nature of many small US record labels in the 60s and 70s, and claims to know the absolute and definitive story of issues/boots/legal reissues/second issues on any given record are (I think) sometimes on thin ice.
What is a known 'fact' today is often disproved tomorrow by the emergence of unanticipated new evidence.