There are almost as many methodologies as there are bibliographers. You also find that in fine art. There are whole discussions about how a catalogue raisonne should be compiled. What is authentic, legitimate, authorised, etc? These are philosophical and semantic issues and what the compiler thinks influences how s/he works.I would assume a good bibliography wouldn't concern itself with the "legitimacy" of the publication, but rather that it exists. There is a lot of "questionable" stuff in Krumhansl. Of course I have no idea what a bibliography is supposed to do, since a lot of bibliographers seems to make up their own rules of inclusion.
Lots of iffy stuff to these. If the compiler happens to need cooperation from the estate, sometimes that estate strongarms the compiler into excluding certain unauthorised or "damaging" material in return for permissions. Sometimes the subject conceals material. There is an amusing letter from Larkin to his bibliographer asking if he is duty-bound to reveal the most turgid pieces of rubbish he published as a student or whether he can conceal this material. I don't recall what reply he got.