If you can see sidewall cords, replace the tire. Otherwise run it. Modern tires check worse than real rubber ones did, the circa 1968 tires on my 49 Dodge rims are in better shape than the circa 2001 ChengShin on my Savage...
For that matter, the stock, from the factory 1949 issue spare isn't checked at all, don't think it has ever been out of the underbed carrier...