Jeff, It's my understanding that you surely know your stuff.... so I respect your comment and will give it some serious thought. That said, the PNs I found on my fenders, to the best of my understanding, are not the service PNs similar to the examples you provided Rather, they're the assembly line or engineering PNs. Every bit of info I have collected for this particular car (15yrs of data collection), including the photos and phone discussion I've had with you, tells me the fenders are the original pair. I am, however, human enough to admit I don't know everything and could certainly be wrong. If someone before me replaced these fenders, they must have gone through a lot of work to find a pair with the same stamping date (matching all of the other dates on this car's sheet metal within one week) -and- they did so with a pair of fenders having only one coat of paint on them, the same color as the rest of the car (I stripped the car to bare metal myself).
Regardless, I am very interested in Bob's comment. It appears I missed a thread on this subject. Bob, are you saying that in situations where the rocker moldings were options, there is evidence that in those cases there were rectangular retainers were added to the fenders?