Originally Posted by Ralph Sir Edward
Do you mean 1922? And also such works that from 1923 to November 1956 that didn't have their US copyright renewed? (Just trying to be a purist.)
If not, could you explain the 1927 date?
The rule of the shorter term was abolished in the UK in 1956. At the time, the US had a 28-year, renewable, copyright term. Hence any work published prior to 1928 (1956 - 28 years) which didn't have that 28-year copyright renewed, entered the UK public domain. (As you say, that effectively means everything published between 1923 and 1927, since all works published in the US prior to 1923 are in the US public domain.)