To add -the same thing can be applied to most the parts used on the cars. They would not typically have part number stickers /stencils on control arms, exhaust, etc. The sticker /stencils look cool and may indicate a new fresh part(which is impression some are trying to impart) but is not the typical way the car would look from the factory.
Bob - I agree but have seen some really old and original looking sticker labels on the back side of original untouched fastback fiberglass panels. Also there is the gas tank sheet metal stamping that occurs in various locations (sometimes not at all) on original tanks. I would consider those to be correct. And I do recall seeing/reading about some driveshafts that might have had some original stencils. Just trying to paint (pun intended) the complete picture on stickers and stencils.
So to tabulate where stickers and stencils could be correct:
Back of interior fiberglass panels (label)
Back of door panels (stamp)
Gas tank (sheet metal supplier stencil)
Drive shaft
Where they would not:
Sheet metal
Suspension components
Exhaust components
Thanks, John