Berne convention only constrains a life+50 copyright. For example, in Canada (signee of the Berne convention), Prokofiev (dead 1953)'s works are in the public domain.
So why would Berne convention force USA to remove "Peter and the Wolf" from public domain?
I'm no expert and I could be reading it wrong, but from what I understand the treaty allows for the "rule of the shorter term" though wikipedia states that not every country has "accepted this rule."
