Things are complicated by the fact that most of the music is copyrighted not by authors, but their publishers (most of them grouped in a handfull of global media conglomerates). "50 years after composer's death" rule still applies, but then Sony Classical or whoever will 'protect' the particular performance of a LvB's symphony, when the work itself is in public domain.

It should be noted (as has been here a number of times) that currently 'fair use' doctrine seems to be stronger in Europa than USA, but I am affraid that is eroding, too.

Perhaps someone with more knowlege on this than me could write a FAQ entry? 'Fair use' doctrine and RIAA'a attempts to squash it would be most interesting topic.