Dumb question: why do some promos say “P” and a lot don’t?

Seems like an arbitrary thing, but I think it might actually be more significant than it seems, at least something of note for investing.

Promos in TCGs have historically done very well. The only thing with One Piece, it’s not always obvious something is a promo at a glance, because many of them aren’t labeled “P”. I’ve seen a ton of promos with “SR”, “UC”, etc.

Obviously for us on this sub we probably have been exposed more to cards and know which are which. But for your average casual buyer, they might not know something is a promo. Which might have some minor implications on how well certain promos sell.

I’m a big promo investor. Not super concerned about it but I guess I am just curious why some promos are signified and a lot of them aren’t?