NOT IN RIC
UNLISTED ISSUE. Sutherland mentions this issue in footnote 1 on p. 288: "Rare coins exist for Diocletian as Augustus and Constantius as Caesar in the group: cf. N.C. 1955, pp. 68, 72 [...] and N.C. 1956, pl. 15, 4 [...]. Regarded erroneously by Carson-Kent (N.C. 1956, p. 107) as 'probably no more than a variant' for P, ST, these marks are certainly transitional, anticipating the first marks of the Second Tetrarchy immediately before the abdication - possibly unexpected (cf. N.C. 1955, p. 72, n. 11) - of Diocletian and Maximian was announced". But Sutherland was aware only of one coin for Diocletian from officina P and one for Constantius from officina S. The full issue was described by Aleksander Jeločnik (see: Jeločnik, A., "La dernière émission des folles de la première tétrarchie de l'atelier de Ticinum", Revue numismatique 1965, pp. 236-240).
Coin should be listed before TICINUM 55a.
TICINUM [before 55a], DIOCLETIAN, UNLISTED ISSUE, OFFICINA P
TICINUM [before 55a], DIOCLETIAN, UNLISTED ISSUE, OFFICINA S
TICINUM [before 55a], MAXIMIAN HERCULIUS, UNLISTED ISSUE
TICINUM [before 55a], GALERIUS MAXIMIAN, UNLISTED ISSUE, OFFICINA P
TICINUM [before 55a], GALERIUS MAXIMIAN, UNLISTED ISSUE, OFFICINA S