Yes, AT for
Antioch is odd, but according to Lech Stepniewski's
NOT IN RIC (hosted by
Forvm), this interpretation has
good authority, having been proposed by Pierre
Bastien:
HERACLEA 50. This Heraclean issue does not exist. The
mintmark should be read SMATA (
Antioch mint), NOT SMHTA. See Pierre
Bastien, "Coins with a Double Effigy Issued by Licinius at
Nicomedia,
Cyzicus, and
Antioch",
Numismatic Chronicle 1973, pp. 87-97, plates 5-6. See also ADDENDA,
VOL.
VII,
ANTIOCH [before 34]
LICINIUS I &
LICINIUS II, UNLISTED ISSUE,
OFFICINA A-H.
To cite
Bastien, p. 94: "The abbreviation of
Antiochia to AT obviously seems unusual,...but must be accepted as an unquestionable fact. We have come across specimens from eight
officinae (1st-8th), whereas at this period
Heraclea had only four
officinae at its disposal."