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
https://en.wikipedia.org/wiki/Wikipedia_talk:WikiProject_Dictionary_of_Nati…
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