Debrett’s, look him up in:

Since 1780 (with a few lapses) Debrett’s Peerage and Baronetage has been the who’s who of the English titled, and you see it referenced in Persuasion: “Sir Walter Elliot … was a man who … never took up any book but the Baronetage.” The entry mentions his name, birthdate and title, the date of his marriage and his wife’s name and her death, and the birthdates and names of his children. If someone claimed to be Lord So and So, you could look him up in Debrett’s. Holmes, of course, looks up clients and suspects in a red volume that is possibly DeBrett’s, but it is not specifically Canon.