Trims break surface topology. Take a look at my file. UV coordinates inherently extend to the full domain of the underlying surface. A trimmed surface is actually a Brep class and not a Surface class
Depending on how you want to reduce those wafers at the cut-open, you may do something similar to what I have and “dispatch” out the ones lying “outside” of the surface trim. It’s a start, but you may get a jagged edge if the wafer is too big.
forum_trims.gh (149.0 KB)