Life + 70 applies in the EU and in the US only for works published after 1978, while Canada (where IMSLP hosts a RVW page) is governed by life + 50. Old 100th seems to have been composed for the 1953 coronation, and if registered or published that year would have been up for its first renewal 28 years later and potentially protected though 2048.
I was just hunting for the first edition of SINE NOMINE and found IMSLP's English Hymnal scan is somewhat redacted. To see the 1906 print one can from the US go to the Hathi Trust site. I was very much startled by what I found: "Thou wast their rock" begins with a half note, for just one example.
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