If one reads his explanation of when these "signs" were acquired?...
Unless my memory is totally shot (which may be true)... I seem to remember some other "South of the Border" Sellers that claimed to have "found" a number of items that were "mis-prints, seconds, etc... in the 1980s... That they had set aside... I believe that "Wholesale Candy Shop" (or something like that) and the Guy from Mexico, that kept changing his Seller ID; used a similar if not exact line... "That his signs were picked up in the '80s" and he still the invoice for them....