This too is a genuine Constitutional issue. The issue is whether or not Congress has exceeded the power granted it by the people through the Constitution. The Constitution is plain -- it grants Congress the power to create copyrights only insofar as Congress limits that copyright to a specific period of time. It even states the reason. The reason copyrights are even allowed in the first place seeing as the very idea conflicts with the First Amendment, is that granting a limited copyright will stimulate an artist or author to create something in the first place. In no instance can a retroactive extension of a copyright term stimulate something's initial creation. Given that fact, Congress exceeded its authority.
Do you believe that Congress is unbounded in what it can do?
I salute you for having come up with an argument that is stronger than "my internal definition of the word 'limited' is correct, and everyone else's is wrong." I wonder why your argument did not carry the day.