When I set both lines side by side I realized something I hadn't noticed before: Shade writes a poem about "life as a poem," whereas Kinbote's footnote is about "life as a footnote" Neat.Kinbote's rendering is equally applicable to TOoL, although who authors the "unfinished masterpiece" remains undisclosable.
Man’s life as commentary to abstruse
Unfinished poem. Note for further use.
(John Shade, PF,lines 939-40)
“…our poet suggests here that human life is but a series of footnotes to a vast obscure unfinished masterpiece.”
CharlesKinbote, footnote to lines 939-40)