Fashionphile says serials had seven digits from 1986 to 2005, with the first digit giving the series, and eight digits from 2005, with the first two giving it. coutureusa.com puts the same break between the 9 series and the 10 series.
Christie's says that before 2021 Chanel bags were identified mainly by the sticker and its card, and that from 2021 the house gradually introduced microchips. Xupes notes that a bag from 2021 can carry either.
The chip sits in a small metal plate. Fashionphile says the plate starts with a letter, always has eight letters and digits, and has no known link to the year the bag was made. coutureusa.com describes a seven-character code, so the two guides differ on its length. The decoder reads a plate code as the microchip era and gives it no year.