On the Special Edition of this series, the serial number is engraved on the clip ring, while on the Limited Edition variants it is mostly placed at the end of the pen. The rollerball also bears its number at the end of the pen. A complete absence of the number would be untypical; usually the supposed absence is simply an overlooked engraving. The 1906 edition comprises correspondingly numbered examples, which secures the authenticity check via the correct numbering.