I would assume they didn't spring the release on the public out of nowhere. I don't know when they first revealed it was coming, so maybe there was a gap where it appeared the N64 was done. Determining when a system is dead is more a matter of hindsight. The public is rarely told that a game will be a platform's last official release. But once the public can determine that, we know where it ended. Personally, I'm not going to come up with some arbitrary amount of time that has to pass with no releases before I call a system dead. If I call a system dead prematurely, then I'll correct myself when that information presents itself.