In UK law (which applies to me) copyright lasts for 70 years after the death of the writer/composer, which means right now they have to have died before 1943. (For recordings, it's 50 years after first publication.) For instance, It's a long, long way to Tipperary was written in 1912 by Jack Judge (d. 1938) and Harry Williams (d. 1924) is OK, but Goodbye-ee was written in 1916 by R P Weston (d. 1936) and Bert Lee -- who lasted till 1946. Quite a few of the writers or co-writers lived to a ripe old age. (Maybe there's a link -- good news for some of us!)

Q, you're right! Peter, the fighting stopped in '18, but the official end was in '19, which I still find confusing. (And it started in 1914, not 1917!!)