About 3 fry from my mustard gas HMPK x copper HM spawn have DT...unfortunately, very uneven lobes :(

This means that both the HMPK and copper HM carry the DT gene, correct? I won't be breeding any of the DT fry, but if the color and finnage turn out well, I want to breed the other fry. More chance of uneven DTs?

Breeders cross HM longtail & plakats to DTs to improve the dorsals, which in your case worked because, if this male is the one pictured in your other posts, has a very nice dorsal. They probably weren't selective with the eveness of the DTs lobes since they were crossing to improve the dorsal and weren't looking for any future DTs from the cross. Since these three offspring have uneven lobes in their tail, I would suspect that future spawns would produce more of the same, however you never know for sure. The next spawn might produce some champion DTs. I would choose the candidates for the next spawn with the intentions of improving the plakat line and if you end up with some nice DTs out of it, just consider it a "Happy Surprise" :D

It is all depend what you want to breed and what you looking for. I would hold onto the juvies until they mature. You might want to cross them to a singletail to get nicer and bigger dorsal. :D