mistakes happened all of the time back in the old days.
i had a 71 340 cuda HT car that had NO #'s stamped into the body. nothing in the cowl or the radiator support.
What you had was a body in White car, which was usually given to factory sponsored door car class racers ,stock, SS, modified eliminator, gas class, and Pro Stock for them to make a class legal car without having to strip a complete car to start with
Most of them would have been chemically strip, acid dip maybe also
before starting the builds on them. they where bare shells with all the sheet metal sent along with them for the racer to assemble the way they wanted them to be fit up
That was a good find