I'm saying their intern who doodles their maps put the wrong name down, because if they WERE going to recon something about the map they wouldn't have left off Karthwasten and Dragonstar. To that end, the first pge didn't have Whiterun, Markarth Side, Snowhawk, or Dawnstar, so I think it's more likely that they haven't retconned anything, they're just screwing up.
why wouldn't they? Dragonstar is part of Hammerfell according to the empire, and is listed in that province. Markarth is mentioned in the 1st PGE's section on Thu'um, so i think it is likely they decided to scale it up to city level rather than making up lore for Snowhawk. Besides, 440 years have passed between the PGEs - is it really that hard to imagine that cities have risen and fallen during that time? I find the growth of Markarth and the decline of Karthwasten much more interesting than "an artist screwed up and the editors didn't catch it." If you're going to argue over any new lore that contradicts old lore (Tamriel-as-a-D&D-setting lore, at that), we're going to be here till we both die.
P.S. i object to your view of cartography as "doodling." i suppose the whole PGE was written on a napkin during a lunch break?