Questions about 1965 Lincoln Cent labeled "Double Dot"

Anyone here have any background on these? Recently came across these which were labeled as such on the old yellow 2x2's. Thanks in advance.
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Member ANA, SPMC, SCNA, FUN, CONECA
Usually an extra dot appeared next to 'E Pluribus Unum', hyped up in the 60's, worth no premium.
This.
Harry Forman, and Fred Volmer back then.
I hadn't seen one in at least 15+ years, then bought
one in a collection - put it up on Ebay, and on May 31,
it sold for $18.50. (raw BU)