I googled for "cyphral distich" before:2026-08-30, and found barely anything that was relevant. Mostly incorrectly dated pages about this exact thing. In fact, the only instance I can really find is this website, which seems to be an archive of a magazine issue from 1927 https://toebes.com/Flynns/Flynns-19270813.htm (it also has a scan of the original text of the magazine in the top right). This facebook post https://www.facebook.com/groups/2600net/posts/46775529324677... seems to indicate it is found in at least one edition of the book