The reregistration only works once, and it is presumably in the bill because that's how copyright worked a century ago. You got a 28-year term. If your work w

The reregistration only works once, and it is presumably in the bill because that's how copyright worked a century ago. You got a 28-year term. If your work was still worth something after that, you could get one more term -- but because you had to file for it, only works that had commercial value were likely to get renewed, which meant that the public domain grew more rapidly than it would under a single 56-year term. Most works are actually abandoned by the end of 28 years, and this way someone else could pick them up.