Cheers from Chicago guys. This thread is amazing. I was up until 5AM reading through it.
We just got a couple of these weird red-tailed dottybacks in, alongside a more typically-colored specimen. I agree that they're not P. flammicauda. I haven't heard back from Dr Gill on this yet, but I'm pretty confident this will turn out to be a variant of a somewhat common species. The opercular markings are the giveaway.