@height8 This is very strange, and I may have solved my own problem: in Mendeley, a lot of my "é"s take 2 backspaces to delete — same as the question marks that come up in BBEdit. First backspace transforms é -> e; second deletes the non-accented e. If I retype the é using opt-e+e as I usually do, the .bib file as opened in BBEdit displays properly-formatted LaTeX accented characters.