I've wondered the same thing about Woody's Columbia River songs. Sure as heck seems like they should be in the public domain, since the taxpayers paid for them. I suppose it depends on the terms of Woody's contract.
I suppose Sonny Bono's 1923 endpoint will never be changed in the United States - I think songs published after 1923 will be 140 years old before they become public domain. Once Congress gives the corporations a gift, it never takes it back.

-Joe-