Bryson’s items on Halitosis, Psoriasis, Gillette, equivocal Edsel (I borrowed the book for a couple of minutes, only) suggest that Nabokov, in Montreux, chose a particular decade or two (twenties, thirties) for his “historical/actual” references. For a meticulous researcher as he, if this information proves to be correct, one might expect him to be pointing to something  related to Shade’s emotional world.  The poet’s love for Hazel always strikes me as false: if there’s any “pathos” it might be related to guilt feelings towards an event that would have happened long before the young woman committed suicide. Shade always returns to the sweet sentimental “swing” (a child’s plaything!), while he informs us that it hung from a tree which has grown considerably over the years. Were it not “a phantom swing” it would then be hanging from high up among the branches…  This is why it has just occurred to me that Shade could be indicating a special period during his daughter’s infancy (describing dated adverts and returning over and over to a “phantom swing”).