1976 Bicentennial Half Dollar Error?

No MM usually means a grease-filled die and "filled mintmark" is just a die chip.


If I understand your question, then here:
https://doubleddie.com/919455.html

Having researched bicentennial variety coins, I understand his conundrum. The Wexler catalog lists three DDO for 1776-1976 Kennedy half dollars. All three entries consist of a title with no images or text. My assumption was that they were prior entries that might have been delisted and deleted, or perhaps placeholders for submissions that turned out to be MD/DDD under close inspection.

Much of the 1976 stuff on ebay is, to put it bluntly, rubbish. The bicentennial coins seem to draw the goofiest listings for "error coins" and the magical trio of DDO-DDR-RPM.

Regarding die clashes specifically, I don't know about 1776-1976 Kennedy half dollars, but there are definitely clashes on drummer boy quarters. Given the huge volume of 50¢ coins struck, I would find it implausible that zero clashes made their way into circulation. Clashes still happen on current model coins all the time, and the Mint is not scrambling in a mad rush to get them out the door by a hard deadline.

Just saying since you mentioned ebay: The vast majority of listed doubled dies and RPMs do not bring premiums in the actual hobby. Nor do most clashes. This is a hard lesson people who buy from ebay find out when they go to sell what they were told was a good error coin.