The date I heard was 31st December, 1922. On the one hand that information could be out of date, and one would expect it to move forward a year per year. 1924 could very well be right. On the other hand governments keep extending copyright duration, and grandfathering in older works (at one stage there was actually a bunch of stuff that went out of copyright, then came back in). At any rate, it's some time in the early 20s.Twinge said:It is [...] free to use if it is [...] made before 1924 (I think that date is correct, could be wrong...)
But... (ah, there's always something... ) there are exceptions. In the UK publication of the KJV Bible has to be authorised by the crown. Lily's Latin Grammar has some kind of similar status. More famously the Great Ormond Street Hospital for Sick Children has perpetual rights to royalties on Peter Pan performances - this exception is actually written into UK copyright law.