Thanks to macropod/Paul and Guessed/Andrew. I'm also not a Selection junkie at heart, but my many prior attempts using ranges fell flat, and debugging felt marginally simpler with the text visible. HOWEVER, both of your replies indirectly pointed me to the actual root of the issue, which is:

This document -- and apparently all of the others in which my original code routinely failed -- contains fields whose results contain parens, and those fields confound the adjustments needed to check for italic font within the parens. (Sure enough, the Execute loop went south right when it got to the first such field. Agh.

I haven't fixed it yet but it should be straightfoward now. Thanks so much to both of you.