Interesting. I could see the merit of such a theory also.
So maybe 326-327 more likely than 328, you'd say?
No, because then you would have to discard (or seriously rearrange to squeeze in) all the coinage before the DAFNE issue-- GLORIA EXERCITVS, GLORIA ROMANORVM, LIBERTAS PVBLICA, and SPES PVBLIC.
edit- I added comments below anticipating further debate
I will elaborate on why you can be pretty certain of the order of issue. First of all though, the date. Lars is not the first person who believes that mint production started earlier than Bruun. Speck and Huston in 1992 in their pamphlet
Constantine's Dafne Coinage at Constantinople, wrote that the production for DAFNE coinage needed to start in mid 327, versus the date of 328 in RIC; meaning that the mint would have opened a few months earlier than stated in RIC. This topic is starting to bog down on dates though when it should not. There is no point in trying to link events of 326 with the anepigraphic DAFNE and Helena coins which must have been minted around two years later, so circa A.D. 328 if you must date it.
Start with the new types minted just for Constantinople-- GLORIA EXERCITVS, GLORIA ROMANORVM, LIBERTAS PVBLICA, and SPES PVBLIC issues ( there was also short run of Constantine I campgates prior to these coins, which might have lasted a few months) Say that minting started around mid to late 326 and given the quantity available, ran to around mid 327. These types undoubtedly came before the DAFNE issues because of the transition of the bust types. At first all these coins have the laureate bust, then change to the diadem. All the DAFNE coinage, starting in mid 327, is diademed, so they definitely came after these issues. The first DAFNE issue could not be the anepigraphic type either, because the first type is RIC 30, a head with diadem, which is the exact same bust type as the four previous diademed issues. So the anepigraphic issue comes after RIC 30, which would at best be late 327 - early 328, if you put the anepigraphic before the other eyes to heaven coins (RIC 32) and a bit later if you put the issue after...either way enough time separates the vicennalia of 326 from the Helena and DAFNE issue that it seems very unlikely that there is any connection.