Q. In MLA format, when I'm citing multiple, separate pages from a source, do I list them all in the in-text citation?

Yes, if what is on both pages 16-17 and 19 are being discussed in the same sentence.

If in separate sentences but same paragraph, you'd need two citations, one with Wadsworth in parenthetical reference:

blah blah blah (Wadsworth 16-17). blah blah blah (19).

If they were two separate paragraphs they's each need be complete:

blah blah blah (Wadsworth 16-17).  blah blah blah blah blah blah

blah blah blah (Wadsworth 19). blah blah blah blah blah blah