I know the one you mean (does that mean I'm getting obsessive ?)

I can't be sure, but they probably date to the 1970s. If you have the size that will help (but not always) and the thickness if possible. Chance and Fiesta used a uniform 3mm glass for these trays, and this is quite common for virtually all slumped ware, so a thicker glass might indicate another manufacturer (Houze, Duro-Ray, etc)