A separate point. I am genuinely interested in hearing what others think of Shade's alleged relationship with his student, the girl in the black leotard.
Q. Explain to me again, how do we know that Shade has a mistress?
R. Shade tells us that "Aunt Maud lived to hear the next babe cry." Kinbote correctly points out that this can hardly refer to Hazel but by implication this "next babe," born in her later years, must be a blood relative of Maud's. The only people capable of engendering a child who would be related to the elderly Maud are Shade and Hazel. Since there is no apparent (sorry) child who fits this description in Shade's poem, he or she seemingly no longer exists or has moved out of Shade's orbit and certainly has not been recognized as a legitimate child or, in the unlikely event that Hazel is the parent, grandchild.
I went looking for a child fitting these parameters, and found that Shade had put him and his mother in Canto II as the "other love" of a widower at IPH and her son who died together in a head-on collision on a wild March night. This child has a mother who is not Hazel, so by deduction Shade must be the father. The mother, the blonde in a black leotard, was a student of Shade's and she is said to "haunt Lit 202." This turns out to be literally true, since "the other love," "die Mutter mit ihrem Kind" and the blonde in a "ballerina black" leotard all refer to the same person, a former student who committed suicide taking her child with her in an automobile "accident."
Kinbote, as Shade's alternate personality, knows all this, and Shade too we discover is aware of what happened to his paramour and their child. The moments before their deaths are described/imagined by Shade in the travelogue he and Sybil watch on TV during Hazel's last date. We know that the "other love" mit ihrem kind died in a head-on car crash on a March night, and the travelogue also describes headlights dilating like stars on a March night [this Shade imagines from the suicide's point of view of course].
Come to think of it, dilation and death are recoupled when Kinbote-Shade dies alone in a god-forsaken motel room.
Kinbote clearly thinks that the dead wife in "ballerina black" (l. 586) is one and the same, and if we trust his account of the dinner gathering, it seems that Sybil was aware of issue.