I seem to recall that he wasn't allowed to use Alien3 stuff in the book for some reason because of some licensing thing, that they'd only licensed 'Aliens' specifically but not any of the other movies. The only reason the Nostromo or Narcissus are in the book is technically because they're in 'Aliens' as well, and while the events of 'Alien3' are hinted at in the final chapter they're not directly referenced by name.