Why would anyone assume the guidebook isn't exactly in the last place it was seen - aboard Quark's Treasure
The Earthlings finds this spaceship and its alien crew - which would be of more interest to the primitives? The ship, which is incomprehensible to them, or the living crew? I'd say the crew would be of more interest than the ship. Yes, the primitive Earthlings managed to look inside it, but why would they remove
anything from it? The first priority was to establish communications with the crew; the ship could wait for later investigation. It's not like the primitives expected to lose the ship and
the crew within a day of finding them. I'm sure they expected to have decades
to unravel both the ship and the crew.
So, given an expectation of years with which to work on the ship, why would anyone remove anything from it? It wasn't going anywhere, and who would know what might cause it to blow up? Better to not touch it.