Performance records for the professional theatres in London remain radically incomplete until 1705, when the managers of the two companies decided to pay for advertisements every day in the Daily Courant (est. 1702). Few scholars understand just how incomplete and patchy the surviving records are. For 1660-1700, of an estimated 14,067 total performances, we have title and exact date for just 949 (6.7%). From first-run norms and anecdotal evidence about success, we can infer about 1502 additional performances (another 10.7%). We have no information about 11,616 days (82.6%). Fully 79.8% (758 of 949) of performances derive from just five sources: Pepys (342), incomplete bills for royal attendance (255), Sir Henry Herbert (57), Nell Gwyn (52), and Lady Morley (52 prior to 1701). Letters, other diaries, marked copies, and miscellaneous sources supply the other one-fifth of what we know. There are huge variations from season to season. In 1667-1668 we know 120 of 496 estimated performances (24%), but in 1669-1670 we know only 7 of 328 (2%). In 1678-1679 we do not know a single definite title/date for either company. Approximate premières for more than 200 plays have to be established from what is known (if anything) of the date or approximate date of publication. The number of performances that happen to be recorded often bears little relation to what we know of either the immediate popularity or long-term success of particular plays. There is a moral here: theatre historians need to remember what is not in the surviving record of performance in London. [ABSTRACT FROM AUTHOR]