What year car do you have ? Reproduction fenders are intended to match all models. original fenders where the same for all models - The only difference is where the trim is mounted (as noted above)& were the holes for the trim is mounted on Belairs vs Impalas in 61-64. No side trim on Biscayne's.
The body lines(style lines) on reproduction 1/4's and fenders and probably doors do not match original parts.
They also as I recall do not match the gaps as well as the original parts.
On a 1963 reproduction fender on a friends car that I finished (after he passed) the top gap on the reproduction 1963 fender was 2 to 3 times wider than a factory fender gap. The car was already painted so we left it that way.
I bet the style line on 61 and 62 reproduction fenders do not match the door style line of a factory 61 & 62 door.
I asked a local very well know local high quality classic car restoration shop about reproduction fenders not fitting and why they use so much reproduction -He said its the time delay finding the original fenders and also their condition (assuming the car owner has not found good original sheetmetal). This was on 69 Camaros they were doing.
He said they tear the reproduction fenders apart and redo them to make them fit, I am sure he would do the same on 61-64 reproduction parts.
The body shop guy has to make the repro parts match the original body parts.
I made the body shop do this to my 62's if I have to use reproduction parts(I had a 62 Impala hardtop rear 1/4 that was done that way) That's why original parts for fenders are always better, even if they need some lower rust repair.
It took me months and years to find parts for my 62 SS 409 convertible but I found original 1/4s, had good doors, trunk and hood and found NOS front fenders.
Paul