"We'll talk of sunshine and of song,
And summer days, when we were young;
Sweet childish days, that were as long
As twenty days are now."

 

So ends Wordsworth's "To a Butterfly"; twenty days span July 2-21, 1959.

 

Has Wordsworth sourcing in Pale Fire been fully adumbrated?
(I mean his writings, not coincidences of birth/deathdates and posthumous preludes.)
(I'm only aware of but haven't access to Sicker's'92 "Pale Fire and Lyrical Ballads" paper.)