Posted By:
davidcyclebackCUDA1966, there are collectors who specialize in these stadium postcards and know much more about them than I. There's a guy on eBay who's very knowledgeble about baseball postcards, but I forget his username at this moment. I'm sure someone else on this board knows it. RTO-something rather. He would be of help. The stadium postcard collectors use serial numbers on the cards to categorize them.
PSA grades postcards that are offically cataloged or otherwise clearly identifiable. Since there are formal collecting groups of stadium postcards who unlikely have compiled much info about them, I would think a genuine stadium postcard would qualify as gradable. The various stadium cards were sold commercially to the public, so they are as much baseball cards as the 1950s Dormand Postcards.