Several of the other FF program numbering systems have produced curiosities. I just noticed the Delta thread today, and recall an entertaining AAdvantage one from The Other Place. The DM numbers have undergone major structural changes. Mine is 7A4D### while Mrs. jb, opened in 2010 has eleven numbers beginning 4006. I have no idea at all when I opened mine but it must have been fairly early in the Agony Airlines days.