As always, thanks Michael. Great information.

Just to understand the differences and advantages / disadvantages, I'll have them send me both a STEP and and IGES file next time, to test.

As for your prescribed steps to try and fix the bad spots, wow! I wasn't entirely sure what was going to happen, but it worked on the exact example file I posted here. I never realized that there was hidden surface data, under the trim parameters. There is still some weird line data in the new piece I arrived at, but the surface itself looks perfect, and if it looks that way once it gets into C4D, then that problem is solved! And, fortunately, it is only in a few spots on the product they sent. Granted, it could be worse on other ones, but if I can go in and try an fix things, that's one less major concern I would have.

Cheers!

P.S. I forgot. One other question. The scale tat which these products are importing is tiny. When I receive the same kinds of product CAD from one of their affiliates who use ProE, the files seem to import accurately at 1:1 in MOI. The NX guys are using inches, but would that account for such a massive discrepancy? Is there something which I should be doing in MOI to counteract that?