I think you've all misunderstood. "Mutts" are uneven/unequal fin forms (eg. CT are suppose to have equal ray lengths) AND OR with a color mixture that's not harmonious (more of an opinion). So VT's are not mutts. They are a specific fin type.
Young VT usually have an oval - square tail shape. As they get older, their tail will curve downwards. These are not mutts.
Some individuals may have a deformity - curled fins. Even the best pair of the same tail type may produce offspring with this deformity. And it is apparent only when the individual fish is fully developed.
A once sick betta may have clamped fins which sometimes can't open as it should when it is better or at least needs a long time to redevelop its fins.
These are not mutts.
In short, the bettas posted, IMO, are not mutts. They are simply several varieties of VT.