This is a state-of-the-art answer to a question that has come up in the past: how much of the Dictionary of National Biography on Wikisource is out of copyright in the UK?
I was prompted on this today, and realised we can now do the business properly (Petscan). See
Talking about the DNB first edition, which is US public domain, but applying the 70 year rule from death of author for UK copyright, a list of 32 authors results. That is around 5% of the 600-odd authors, but the affected proportion of articles will be noticeably less (complete listings are on the Wikisource author pages). There are usually caveats, and here there is a working assumption that we have a death date for the author. There will be a few more where Wikisource has failed to research such a date.
Charles