I first herd the term in New Mexico in the 1990s. Old pawn is dead pawn. The Navajo delt with the trading post for more than a 100 years and would pawn anything of value there. Old pawn is a reference to the old family heirloom jewelry put in pawn and never taken out. The term has been very loosely used and misused that I've noticed. Your best to ignore the term and have a better understanding of vintage Native American Jewelry when buying, but so many sellers use the term to gather the attention of buyers and sell pieces that look native made, but are not genuine or even that old.