Curtis Clay on http://www.forumancientcoins.com/board/index.php?topic=114848 at 05:10:36 pm :
“Apparently only three other specimens are known, two of them with a clear S at the end of EXERCITVS.
Bastien 359, pl. XI, Milan. Exergue damaged, but reading [AQ]S seems probable. Last letter of EX - ERCITVS off flan, so EX - ERCITV[M] can't be excluded. From different dies than yours.
Bastien Supplement 359a, pl. S V, BM. Mintmark mostly off flan, read AQP, but AQS looks more likely. ERCITVS on right fully clear. From different dies than both yours and the Milan coin.
Ditto 359b, same pl. S V, Auctiones 10, 1979, 799. Mintmark clearly [A]QT. ERCITVS on right fully clear.
So your EX - ERCITVM indeed appears to be a new legend variety, unless that is the correct reading of the Milan specimen too!“