I checked in RIC VII for each mint that struck this reverse:
LONDON: AD324
LYON: AD324
TRIER: AD324-328
ARLES: AD324-329. Note that the VIRTVS AVGG have been struck for Constantine I and II, Crispus, Licinius I and II from AD325 to ad 329.
ROME: AD324-326
SISCIA: AD324-329
THESSALONICA: AD326-328
HERACLEA: AD316-320. Only for Licinius.
CONSTANTINOPLE: AD326-327
NICOMEDIA: AD324-329
CYZICUS: AD324-330
ANTIOCH: AD325-330
ALEXANDRIA: AD325-330
What we can say with this listing is that we can reject the idea that employees were not told to change or engrave dies from habit. If we look at the Constantinople mint, it start to struck those coins just after its opening, so we can conclude there was no habit and the employees should have been well informed.
As you say, Helena might be the other G but in this case the VIRTVS AVGG reverse from Arles mint seems a little bit strange for an Augusta.