George Shimanovich answered my question on "why do we have to take Kinbote's word", here , telling us that " By questioning everything that Kinbote says we make out of PF what it is not: grandeur puzzle of who wrote this or that part instead of what VN wanted to convey to reader (to me)...If we stop taking authorship game for granted then everything changes. Certain things that Kinbote says can be questioned but only when contradicted by novel’s text directly... Burden of proof then is on a questioner of Kinbote/Botkin’s word. And until the convincing proof from the novel is presented we should stop downgrading that Russian scholar..."
George, I was not questioning "authorship" - for my question was more limited in its scope.
If there is a chronological discrepancy when we compare poem and commentary, one that turns John Shade into a prophet, why not entertain doubts about the commentator?
Remember that Kinbote, while writing about Shade's line 596, brings up avariant that mentions "tanagra dust" ( written July 14th), where he finds an uncanny reference to "gra-dus". Kinbote enjoys a prophecy, perhaps, just like the one that we encounter when we combine two elements ( poem and commentary) on the scene I was questioning: