@jsf, when we see coins with backwards, incuse letters on them plus a coin-sized groove (matching the rim), we call these "vice-jobs" because typically they were made in someone's shop by squeezing one coin between two others in a machinist's vice. I don't think that you have a mint error here.
"If you climb a good tree, you get a push." -----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed." -----King Adz