But are there other half-follis issues known from the 320s? Besides of course the POP ROMANVS commemoratives that were another thing altogether and were minted likely in 330.
There are other half-folles from the RIC VII period, but they are very distinct from the Helena coin and issued for specific reasons, like the FVNDAT PACIS and GLORIA PERPET types issued from Rome in A.D. 313 to commemorate the defeat of Maxentius. There are the posthumous issues like MEMORIAE AETERNAE Divus Maximianus coinage issued A.D. 317- 318 from Rome. The Helena coin, besides being issued along with the anepigraphic Dafne, may have also been issued for her 80th birthday. We do not know her actual birthday, only that it was around A.D. 248- 250. So an issue of A.D. 328 for this coin could have fallen on her 80th...this is purely speculation on my part though and does not lessen the chances that this coin was struck along with the DAFNE issues. Another thing that convinces me this was issued around 328, is the mintmark in left field, which is like the DAFNE issue (and all Constantinople issues from 327- 328) but completely different from the POP ROMANVS coins circa A.D. 330, with the officina in the exergue. Note also the similarity of the legend, where it starts and breaks etc. So, even if not issued at exactly the same time as the DAFNE coinage, it was issued very close.
Below is a Constantine anepigraphic DAFNE