Synthesized answer
The author, M. M. Bakhtin, has accumulated a "huge storehouse of factual material" which he has analyzed, reflected upon, and reconsidered throughout his lifetime [cover page]. This material forms the basis of the six short works presented in "Speech Genres and Other Late Essays" [cover page].
The passages do not specify what this factual material consists of, only that it is extensive and has been the subject of Bakhtin's lifelong intellectual work [cover page].
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Speech genres and other late essays by M. M. Bakhtin Description: "Speech Genres and Other Late Essays presents six short works from Bakhtin's Esthetics of Creative Discourse, published in Moscow in 1979. This is the last of Bakhtin's extant manuscripts published in the Soviet Union. All but one of these essays (the one on the Bildungsroman) were written in Bakhtin's later years and thus they bear the stamp of a thinker who has accumulated a huge storehouse of factual material, to which he has devoted a lifetime of analysis, reflection, and reconsideration."--Page 4 of cover.