69 camaro - GM gas tank vs repo

[enio45]

A while back I bought a load of NOS 69 Camaro parts and in the lot was a new gas tank. There is no GM sticker on it so I was wondering if there is a way to tell an orig GM NOS tank vs a repop. Most of the NOS parts were purchased in the 80's so I assumed the tank came from that time period as well - however how do you tell if it is NOS GM?