SR18 was misprinted, the back was identical to SR16. (See https://www.broccoli.co.jp/topics/080229_toreca_nanoha.html for images). You could exchange this card for the “correct” version, so two versions of SR18 exist. [Archived: https://web.archive.org/web/20200908164657/https://www.broccoli.co.jp/topics/080229_toreca_nanoha.html]