That's pretty much where I was at. I think I looked at every photo of both species. I did get a few photos of the underwing, but they were not very good. I'll see what I can dig up. Is there a meaningful difference between the two that I should be looking for?

P. progne usually has smaller black spots on the front wing and small more contrasting light spots near the edge of the hind wing (but that doesn't help much if the light spots aren't even there). Also, the dark spots near the base of the hind wing are usually more developed on P. comma, and the dark border (in the dark form) is usually narrower in P. progne. The wings usually look a tad more irregular in outline in P. progne.

On the underside it's usually a piece of cake. In P. progne the pattern is dark gray-brown to dull brown parallel lines, looking rather striated, with the comma mark on the hind wing small, "L"-shaped and only very rarely looking swollen or hooked at either end. In P. comma the pattern is more irregular looking below with cross bands appearing wider, usually in richer browns with hints of yellow, and with the comma mark a bit more curved, larger, and swollen or hooked at least one (usually both) ends. Some females with very plain markings below are difficult to tell apart, but the comma mark and the outline of the stripes (even without any contrast) will usually do the trick.

Unfortunately, in the only shot I got of its underwing, the hindwing is obscured, but the forewing has very similar markings to the one in this image:


I think it's enough to call it Polygonia comma.

Thanks again for your help.