how to tell original vs aftermarket inner fenders

[bigrigpardo]

i just bought a big load of parts from a guy and it came with a very decent set of inner fenders only 2 small spots of rust between the 2. but I am not 100% sure if they are originals or not. are there any tell tale signs to know a repop? I would like to keep them for my resto down the road but only if I can be more certain that they are correct and will fit. I seen a repop one on a truck I sold and it fit like crap.