POV In CIF etc I

POV is point of view. CIF is James Blish's Cities In Flight Tetralogy.

James Blish knew the importance of point of view in fiction and, as William Atheling Jr (his pen-name when writing science fiction criticism), adversely criticised a short story in which POV jumped arbitrarily between characters, even, apparently, entering a dog.

If, according to the rule that has emerged for the writing of fiction, either an entire novel or, at least, each chapter or discrete chapter section is narrated as from the POV of a single character, then is any role left for an omniscient narrator? Presumably it is such a narrator that divulges to the reader the inmost momentary thoughts of a POV character? That character may forget such thoughts or die before he can relate them to anyone else.

Nevertheless, the omniscient narrator can remain so much in the background that we are unaware of (which pronoun is appropriate?) presence. To make a comparison with stage drama, he (since we must use some pronoun) not only never comes on-stage but is not even an audible voice from off-stage. He is more like the director without whom the play would not have been performed but of whom we do not even begin to be aware during the performance.

Knowing all this, Blish nevertheless has some transactions between POV and, apparently, an omniscient narrator. "Common Time" is and can only be narrated from the point of view of Garrard who is alone in an experimental interstellar spaceship and, for some of the time, unwilling or even unable to move. Nevertheless, section 3 begins:

"That Garrard did not die completely...was due to the purest of accidents; but Garrard did not know that. In fact, he knew nothing at all for an indefinite period, sitting rigid and staring..." (Blish, Galactic Cluster, London, 1963, p. 19)

So who is telling us this? The second paragraph begins with Garrard waking and we are back in his POV. The concluding section 4 has three unnumbered subsections. In the third of these, Garrard, back on Earth, discusses his experiences with Haertel and gains some understanding of them. So maybe the passage relating what Garrard did not know at the time represents his POV not at that moment in the story but later when he had had time to reflect on it?