Here's a relatively amusing one. PSA gave it a 'PD' qualifier instead of an 'ST,' so I always assumed it was just a data input error? The coffee (or whatever) permeates both sides of the card. No print defects involved, just some clumsy oaf hurriedly reaching for his remote and knocking his half-caff/decaf over into his box of cards, I imagine...
1973schmidtrc615PSA8PDa.jpg1973schmidtrc615PSA8PDb.jpg
Good news is after some back and forth, they agreed to reholder it at their expense, and now it has the proper stain qualifier attached.