Phantom of London said: "How long does writers copyright last for? I heard once it was 75 years, if this is the case Rogers and Hammerstein Organisation will lose complete control of Oklahoma and Carousel soon?
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If the copyright was registered or the work was published by 1978 it lasts 95 years from the date of registration/publication. If the work was created but not published or registered until after 1978 it lasts 70 years after the death of the last surviving author. I don't know what is considered publication for these purposes.
Its also complicated by the fact that there are separate copyrights on each element of the work (music, lyrics, script) as well as the work as a whole.