As much as this does seem like a bad bill, Congress is specifically prohibited from passing ex post facto laws, so at the very least, "infringing" copyrights that were later de-public domain-ed shouldn't be a violation. It doesn't seem like EFF's statement that "those who have used the works could now be required to pay hefty license fees" could possibly be constitutional, although the fact that they couldn't use them in the future without paying fees is a shame.