Okay.  What you say makes sense.  I'm deriving the idea from the UVs, in which a direct transfer based on weighting after the texverts have been properly split reveals that the corresponding tri makes a difference.  But it wouldn't matter in the case of deltas.  Darn.  I thought I had another morph correction trick.

In Poser, at least, the texvertices are not pre-split for every vertex.  A vertex may have anywhere between 1 texvertex and one textvertex for each vertneighbor poly.  So I have to split and weld the texvertices before I can work with the seams at all.  It would be easier if what you say above were true, and that's what I had expected.

I think I can deal with the problem by sorting through edge neighbors, then.  I have an idea of where I'm going....

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.