[jasonwatkinspdx]

Patent applications filed before the end of 2000 were not published. You can in effect file a continuation as many times as you like, and rewrite the patent substantially as you do. This leads to a tactic called submarine-ing, where you keep filing continuations on a patent that is repeatedly rejected for being overly broad. Then once a concrete target appears on the horizon, you narrow the patent to cover it before prior art, etc is well established.

It's no longer possible to do this with patent applications filed after the end of 2000 due to reform. The period the patent is in force no longer shifts forward with the continuations. But previous applications were grandfathered in.