Anyone find these under your carpet?

[Steve73QMach1]

I have three 73 Mustangs. Two very late production Mach 1s and an early production convertible. Each of them have had these small yellow cap plugs under the carpet on the drivers side rear. It must have been some kind of protective cover for something being installed at the time. Anyone else find these in their cars? The rear seat floor pans seemed to be a dumping ground during assembly. All of my headliner scraps, extra seat bolts, extra trunk brackets, and various other things have been found. Just curious about the yellow caps.

 

[Stanglover]

Yeah, I found 3 build sheets in near pristine condition, 2 under the rear d/s carpet underpad and 1 under the driver seat underpad.