"The Improbable Corrector of Them" appears to be an unpublished Pynchon story apparently dating from 1993. This story about a cabal of NYC proofreaders (formerly writers) does indeed have some of the Pynchon trademarks: paranoia, weird character names, leftist politics, obscure jokes, riffs, conspiracies, enigmatic cultural references, Coltrane, tongue in cheek pop references...