The only reference to 25 years that I know of is in UK law where copyright of words/music remain with the author/composer and his estate for 70 years from death.
However, publishers' copyright (on their layout) is for 25 years. This has little effect where you can't photocopy the music 'til after 70 years after the death of the composer. It does, however, mean that major publishing houses who publish older works will produce a new edition every 20 odd years.
As an example, our church library has oratorios published by Novello & Co. The early ones we have are in Buff covers. 1970s copies of the same music are in Blue covers, and the most recent are in Red.
It is illegal to photocopy the music in the red covers (which are the tidiest copies), but we can go back to the library and find a tidy copy in Blue or Buff covers & copy that as the copyright has expired!