I know nothing about this issue, but from what I can see on eBay, they're from 1978 (not sure if the 1976 was a typo). Here is a list of recent completed eBay listings.
https://www.ebay.com/sch/i.html?_fro...&LH_Complete=1
I do see where PSA did authenticate (not grade) a partial panel. When I did an image search on Google, it appears PSA will give the discs themselves a number grade.
I guess the panels were different colors based on the flavor. Looks like red is spicy, blue is mild and green is pizza flavored.