For mere mortals, I think we've established that female azures of
ladon/neglecta are indistinguishable from ventral photographs. Critical ID characters are associated with males, and especially diagnostic features of the male forewings. Harry may have tips to offer. My own standard is that unless you are in a stand of black cohosh in the western counties, everything after mid-May is
C. neglecta. Your late April observation on iNat is from an area the species progression for which I don't know, but given allowances for how well the colors display on various monitors, Harry may be able to opine based on the open wing in picture 3.
I personally have not seen Spring Azure (C ladon) after April 20, or about when the second C neglecta flight kicks in for real most years. That's true also of Northern Azure (C lucia) in GRSF, although I guess allowances might be made for "refrigerator springs" with long, cool -- but not wet -- weeks in late March and April. We often saw Northern in small numbers on spring counts centered around April 11; this year it was the most abundant azure on the count date of April 4. (although given the newly described lucia iryna we suspect all the material we were seeing in GRSF was this subspecies, see below). I'm sure Harry has better phenology data for the rest of the region. We do have Spring Azure in GRSF, including this year, but almost always either along the high ridge of Piclic Road or along parts of Kasecamp Road, where there are still healthy populations of flowering dogwood.
Same goes for
C idella. Harry may have further info to share -- there's some question I think of how this species is faring with respect to
neglecta -- but again the original paper lays out the (at the time, 1999) understood phenology (see
https://leplog.wordpress.com/wp-content/uploads/2011/03/pavulaan-wright-1999-taxonomic-rpt-on-c-idella3.pdf). Looks like a fairly long flight period that commences after
C. lucia and may extend into May. I would not hold out hope to see any this late in Delmarva; Harry may have additional late dates. My observations have always been in early/mid-April in Dorchester Co.
I leave to Harry all the hard questions, and of course any corrections to the above, including speculations he might not yet have committed to published literature and with allowances that my caffeine hasn't fully kicked in yet this drizzly morning :)