Most 38 year old tubs don't look that good, not even when restored. Based on just how nice that tub looks to be, what looks like new rivets and the color of it, I'd say the tub has been replaced. New GM tubs are a much lighter grey color than what original ones usually appear to be. If a tire has been bouncing around in a tub for 38 years, there's usually marks or wear noticable also.
When new parts are pulled at a GM parts warehouse for shipment to a dealer, a yellow tag is attached to the part or box it's in. These tags are not the part number label that's glued to a box or attached to a larger part (like your tub) by a wire tie or zip tie. These are a pull tag used to identify the dealer it's going too, the date and other information.
I'd guess that what you see on your tub is where the yellow warehouse pull tag was attached to that tub. These yellow tags were never found on new, factory installed parts, just over the counter GM parts. I wouldn't worry about trying to replace it, original tubs didn't have any labeling inside the tub from the factory.
That's my thoughts, but someone else out there may have another idea.
Corvette Store
Sticker on Inside of Spare Tire Tub...?
