All Marcel Proust editions must show an individual 5-digit number (e.g. 12345/20000) at the top in the black precious resin. Only the Hemingway had no direct limitation number but one on the clip without reference to the running number. Even after repairs or exchange of parts, the numbering is reapplied. A real Proust without number would be a unique piece and accordingly worth collecting; however, the authenticity check is to be made carefully, ideally without permanently parting with the pen. Even prototypes are numbered, but with prototype numbers in order to ensure their destruction.