Ubik/WMG

Every event depicted in the story is canonical
The Mind Screw ending comes about because Pat Conley was Not Quite Deader Than Dead after Jory ate her. When Chip fights Jory, Jory is weakened enough that Pat's soul regains its powers and, understandably unhappy with the turn events have taken, rewrites history so she never died. The potential for far-reaching changes was established during her interview, in which she temporarily rewrote the preceding year (in direct contradiction to her later claims that her power was relatively limited. If Jory is to be believed, she thought she was in charge.) This requires that psychic powers can affect the living world from half-life, which is established early on when Jory appears to one of the psychics in a dream. To recap: after the assassination attempt on the moon, everybody but Glen Runciter was killed and put in cold pac. They were placed in the same morgue as Ella Runciter and Jory. While everybody in half-life tried to figure out Jory's Lotus Eater Machine, Glen attempted to contact them. Chip's strong will gave him enough localized power over the hallucination to weaken Jory as described above. When Pat made her move, the timeline changed so that only Glen Runciter died, and Chip, as the executor of his will, attempted to contact him.

Hollister had Melipone killed at the beginning
Jory's family is supported by Hollister's syndicate, and Melipone was payment in advance for the extra strain that Jory would be under when the inertials were added to the morgue. Because the psychic vampires gain the powers of those they consume, this effectively gives Hollister a more powerful agent at a lower overall cost, capable of cloaking themselves from pursuit by prudence organizations.

Ubik was a trial balloon for Product Placement in publishing
Ever seen the artwork for the original hardcover, with the aerosol can? The ad agency for Ubik Deodorant--due to a time-slip poor project management--had, at the time the book was printed, completed only a crude mock-up of its packaging. PKD, unable to maintain his legendary prolific output--facing early confirmation of serious illness from long-term amphetamine abuse--had high hopes for the gimmick's lucrative potential. Sadly, it was not to be. We'll never know precisely what went wrong--unless the Supreme Commander of F.E.A.R. F.E.E.B.L.E. compels Cargill to release their dossier on H.R. Haldeman--but shadowy sources reveal ambiguous (albeit frightening) anecdotes of scalp rabies.