I have already looked at the various threads that are suggested (based on the title of my question), but am not certain of the answer, because I am not using pdflatex or old Type 1 fonts.
I use LuaLaTeX exclusively. Open Type fonts loaded via
fontspec. Always encoded utf-8. TeXLive 2016 or later. My documents are sometimes PDF/X, but are never PDF/A.
For the past year, I have loaded
glyphtounicode.tex plus additional information (ligatures) in my own addendum. But I wonder if that is necessary, or even useful? It does not hurt. However, if the information provided by
glyphtounicode.tex is irrelevant (given the way I compile), then I would rather avoid loading an unnecessary input.
I am not worried about relatively unusual situations, such as pre-Han Chinese or Bronze Age Indo-European.