Fred wrote:-
"The expiry date of UK coypright recordings has been altered from 50 to 75 years, so that won't be the reason."

However, Prestige is an American company - the album was recorded by an American, Alexander Folkarde, and the album was produced by a Scot - Hamish Henderson- and an American - Ken Goldstein - and all the songs are registered as "Traditional".

Furthermore, at the US government help page on length of copyright it says:-


For works first published prior to 1978, the term will vary depending on several factors.

so the copyright position on this album is likely to be confusing, to put it mildly.