Remember that the prank preceded the mainstream web, and MS PR clearly went to great lengths to cover it up. I don't think the internet was "remembering everything" yet at that point
Google's public index is just the short head, maybe even less than 5% of the internet by pages. Old stuff is more or less all pushed out unless its popular.
Google has lost a lot of old posts from those days, but I'd be surprised if it would have lost all of them.