Inside the bag, stamped into leather, is a code that encodes a production period and location rather than a unique identity. Formats have varied — letter-and-digit combinations of differing lengths — and the format itself is the useful signal because it belongs to a window of years.
Pair it with the logo. An accented CÉLINE stamp belongs to production up to roughly 2018; an unaccented CELINE in tightened lettering belongs to production after. A bag whose serial format places it in 2021 and whose stamp carries an accent is internally inconsistent, and that inconsistency is what you are looking for.
The stamp is impressed into leather at an even depth, level, and placed where the model places it. Foil, where used, wears from the high points rather than flaking off in sheets.