So, I'm doing some long overdue inventory clean up. When I looked closer at this coin, I found that I had overlooked a minor(major?) detail. The reverse should read INDULGENTIAE AVG. As you can see, the reverse of this piece was apparently made on a Monday because the "L" is missing. The spacing looks right for it to have been made as such. I can't find another example on line that has the missing "L." Also, the spacing for the reverse legends on other examples with the "L" does not fit this legend. Any thoughts as to whether I have the only unique example of the rookie first day minter's error (haha), or is there a better explanation? CNG's pics
You say "CNG's pictures", allowing me to find your coin in CNG E478, 7 Oct. 2020, lot 527. The CNG description says "From the Benito Collection". So your coin is obviously the identical specimen without the L in rev. legend that Benito showed us in Forum in April 2011, and that I wrote into my copy of Göbl on Valerian etc. on the basis of Benito's post. Though noting the error in Forum, maybe Benito didn't write it down on his ticket, since CNG's description overlooks the legend error. Such a mistake is indeed easy to overlook! I know of no other specimens than yours, but that doesn't mean much since I have never particularly collected or studied the coinage of Macrianus and Quietus. It wouldn't be surprising if other examples turn up, on the market or lying recognized or unrecognized it some private or public collection. I would explain it simply as "engraver's error: one letter omitted from rev. legend".
It’s not terribly uncommon to be missing letters on legends. Keep in mind many engravers were illiterate and occasionally added, lost, or retrograded letters.