Serial Number Tag

I have a 62 b-body and mine is exactly how you describe. Frankly, I don't know how its attached, tho I believe I read somewhere that it is some sort of spot weld.
I think if it were glue, it might have let go by now, 60 years later and God knows how many heat/cool cycles.
You'd think if it was glue that a lot of people would have lost them. BUT back then they didn't care if the glue ate holes in concrete and made you have two headed babies, they used stuff that WORKED. lol It's mighty thin to spot weld, plus, there's no discoloration like a spot weld would do. It's got me stumped. It's not gonna happen soon, but I'm just wondering because the door jambs and under hood areas will be the first places that I repaint.