Z:gnu-www-ja-fdl-1.3-faq--7c4b83-Section 11 imposes two deadlin/en

Section 11 imposes two deadlines on licensees. First, if a work was originally published somewhere other than a public wiki, you can only use it under CC-BY-SA 3.0 if it was added to a wiki before November 1, 2008. We do not want to grant people this permission for any and all works released under the FDL. We also do not want people gaming the system by adding FDLed materials to a wiki, and then using them under CC-BY-SA afterwards. Choosing a deadline that has already passed unambiguously prevents this.