And that Kinbote had told Shade at least some of what becomes the Zemblan parts of his commentary, which influenced the poem.

...

Okay.  Boyd makes two main arguments.  The first is that Kinbote's supposedly homosexual fantasy of Zembla spends much less time on homosexuality (concise hints that he indulged in it in great quantity) than on "women spurned": the allegedly comic episodes of Fleur de Fyler and Garh, and the sentimental, guilt-ridden, occasionally comic episode of Disa.  Hazel was fatally spurned, and she had resemblances to another woman mentioned in Zembla, Iris Acht.  I do find it strange that Kinbote, a paragon of self-centeredness and misogyny, says he resembles Hazel or has time for compassion for Disa.

However, there are other explanations even from Boyd's stance that most of what happens outside Zembla is "real".  What are Kinbote's similarities to Hazel?  Beside a tendency to reverse words, both have been rejected by boys and men--Kinbote by the gardener, who won't or can't have sex with him; and more ambiguously by Bob, who may or may not have had sex with him and maybe purposely got himself kicked out of Kinbote's  house.  And Hazel feels sure most males aren't sexually interested in her, while Kinbote knows most males aren't sexually interested in him.  Also, spending so much time with the poem and admiring Shade so much could give him sympathy for Hazel.

Although as Boyd says, we don't see Kinbote rejecting any women, we know he would, and it isn't surprising that he gives himself the opportunity to do so in his fantasies.  But there are hints that he has done so.  The simplest reading of the problematic passage about turning up "on another campus as an old, happy, healthy, heterosexual Russian..." is that it's a portrait of his real identity, Botkin.  If Botkin became homosexual when he went crazy, he may in so doing have rejected his wife or lady friend.  Or if he didn't have one, he certainly would have rejected the possibility.  A possible hint is that the only non-homoerotic poems he mentions liking are Frosts' "Stopping by Woods on a Snowy Evening" and Edsel Ford's "The Image of Desire", both of which are about fulfilling one's responsibilities despite temptation.  Maybe the passages about Disa in "reality" are based on his continued rejection of his wife or female lover; those about his dreams of her, on the buried Botkin's feelings about abandoning his responsibility to and love for her.  I can't claim this interpretation is certain, but I think it's as well justified as Boyd's theory that Hazel in the afterlife is influencing him.

Boyd's other argument is based on "uncanny coincidences between poem and commentary". His many examples include Shade's waxwing (related to the fictional bird named after his father) that crashed into a window and King Charles's father who crashed his plane into "the scaffolding of a huge hotel".  He notes that Charles Nicol and Pekka Tammi suggested that these are the result of the poem's influence on Kinbote as he writes his commentary, but rejects this possibility since Kinbote recounted his Zemblan delusions to Shade in the two months before Shade wrote his poem.  Instead, he suggests Kinbote inspired Shade; for instance, Kinbote's story of his father's death would have reminded Shade of those waxwings, which give him the most widely quoted part of his poem.  This is how Hazel indirectly inspired the poem--though I don't see that Boyd says she knew about the waxwings and prompted Kinbote to include something suggestive of them in Zembla.

The flaw is that Boyd tacitly assumes that Kinbote's Zemblan stories have remained constant, even to details, from when he tells them to Shade in May and June till he writes his commentary in August, September, and October.  We know, though, that Kinbote can change his story in far less time than that.  He changes Gordon Krummholz's article of clothing four times as he imagines Gordon talking with Gradus.  Maybe more relevantly, he tells us Disa's hair is "coal-black" and "ebony", but then says Shade's description of Sybil, with "dark brown hair", is "a plain unretouched likeness" of Disa.  Before our eyes, he's changed his Zemblan fantasy to make it resemble the poem.  It's as if Nabokov were warning us not to base our interpretation on his reliability about Zembla.

One exception is Timon of Athens.  Kinbote's mentions of it (the Zemblan edition he takes with him when he escapes, Phryne and Timandra as names of the youths he dreams of betraying Disa with, and the re-Englished passage) can't arise from its being the source of the title "Pale Fire", since he doesn't know it's the source (unless he's joking with us).  However, he seems to have a copy of the play in translation as the material for his re-Englishing, and this, not Hazel, may be the reason for the other two mentions.  It may even have led him to mention it to Shade in a story of Zembla or elsewhere.

Of course, Kinbote is one of the most unreliable narrators in literature, and I'd hardly count on his ever having said anything about Zembla to Shade or anyone.