Thanks very much for the comparison pictures. It seems to me that the AU50 has some scratches (although small ones) on the obverse. Obviously, the point at which wear becomes "damage" is a matter of degree. There seems to be genuine uncertainty about assigning grades to this coin. Here are images of a PCGS certified coin (not mine). I'd like to see how people think it was graded. After I get a few replies, I'll post the actual assigned grade. Also, thanks to everyone for participating in this discussion. I'm learning a lot.
I found a great article from the 7/15/03 issue of CoinWorld by Eric von Klinger which attributes the "never punched" theory to a 1962 article by Al D. Craig who designated 4 die types and stated that "dies 1 and 2 never were punched with the Mint mark". However, in 1982, ANACS re-examined the situation and reclassified the die varieties with a new Type 2 which resulted when "a pair of dies producing normal 1922-D Lincoln cents clashed; i.e., came together without an intervening planchet to stamp as a coin. The reverse die shattered and was replaced with a brand new die. The obverse die, not so badly damaged, was abraded (ground) to remove clash marks and put back in service." "This scenario accounted for the combination of weak obverse, strong reverse that would emerge with legitimate claims as a "plain" cent; it truly was missing a Mint mark, because Mint workers, in their zeal to rework the damaged die, had removed the Mint mark." Other accounts, such as the article in Coinfacts.com state simply that "[SIZE=-1]This rare variety was caused when the mintmark became filled with crud on a worn die.[/SIZE]" But there is no mention of die types. von Klinger's article is the most detailed explanation I've been able to find for the "No D" variety. I'd be interested whether some of you have other accounts of this and what you believe to be the truth. Unlike Lt. Daniel Kaffee (Tom Cruise's character in "A Few Good Men", I can handle the truth!