Only a few years ago, 'due diligence' in reading Ulysses or Finnegans Wake boiled down to reading the single volumes of Gifford's or McHugh's annotations, in parallel. To dig any further you needed a serious local library, or a serious investment in book-collecting. (Resumes could be readily padded by publishing emendations drawn from more obscure sources.)
But the progress of Moore's law has dramatically dated this approach. Vast numbers of pictures, videos, etexts, reference works and databases are now freely available via simple Google searches... contributed almost entirely by non-Joyceans! 'Due diligence' now requires exhausting all the obvious resources for a given query, which requires an evolving skill set, as new resources are added daily.
Fweet.org has made a heroic start, but is underfunded and badly needs to add links and genetic layering.
This blog has unexpectedly grown into the only game in town for Ulysses. Its preliminary 'new model' of due diligence includes 'literary pixels' like the signatures of real people from the 1901 census, YouTubes of songs, mp3s of readings and potential mispronunciations, links to mentioned ebooks, contemporary photos, local maps and which side of the street things are on, and of course Wikipedia articles.