RIC does not list this emission with the longer obverse legend, only N C versus NOB C. There was an example in the Bikić-Do Hoard #387; which looks like a double die match to this one. This coin should come before Siscia 99. The reverse has a bit of a double strike, most evident from the muddled S on the altar.
In his analysis of the Bikić-Do Hoard, Claude Brenot, wrote that this reverse was probably struck with an earlier obverse die and calls it a hybrid. This only makes sense if the obverse legend was discontinued; but it was continued with the next emission (which RIC calls irregular) and with the next reverse type—VIRTVS EXERCIT.
Sirmium VIII. Études de Numismatique Danubienne: Trésors, Lingots, Imitations. Monnaies de Fouilles IV au XII Siècle (Rome: Ecole francaise de Rome, 1978)
http://www.notinric.lechstepniewski.info/7sis-99_g.html second picture below
I think my coin might be the plate coin. There are some flan differences that I believe are because the plate coin picture was overly edited and the edges were altered a little. The blurry black and white pictures make it hard to match up little details, but a lot is looking the same.
Constantine II
A.D. 319- 320
18x19mm 3.5g
CONSTANT-INVS IVN NOB C; laureate, draped and cuirassed bust right.
VICT•LAETAE PRINC PERP; two Victories stg., facing one another, together holding wreath inscribed VOT PR on altar inscribed with S.
In ex. ΓSIS✶
RIC VII Siscia –-
Ex-Peter Weiß