The first twelve editions used descriptive notation to record the moves, and only with MCO-13 in 1990 did the series begin to use the now-standard algebraic notation. The most recent edition, MCO-15 in 2008, was written and edited by de Firmian.

Since 1980, there have been other one-volume opening encyclopedias to rival MCO: Batsford Chess Openings (BCO) in 1982 and 1989, and Nunn's Chess Openings (NCO)