This happens a lot! For example, at the appendix of an advanced book on PDE (e.g. Evans') you find a three-page summary of main definitions and results in integration theory and L^p spaces. Or at the appendix of a book on differential geometry (e.g. do Carmo's) you find a succinct compendium of elementary differential calculus, explained in the most efficient way. These kind of condensed summaries, or fascicules de résultats, are rarely found on books that deal with the subject matter directly.