Haha. I know what you mean. Some of my older fanfiction is now inaccurate since the release of HTR13 when all those dates were assigned. I wrote one fic all about L's birthday (in three different years) but now that doesn't hold water. I guess it can be useful for a timeframe, but it also can tie you down! I've also read a number of fics where the task force celebrates Light's birthday during Yotsuba arc, or L doesn't know his real birthday (aw, poor orphan.. except, he does.) But yeah... doesn't work. I remember being uncomfortable with writing a Christmas fic, pre-Yotsuba, where L and Light are chilling because I know they wouldn't have known each other then! XD

Light turns 25 in the second arc? I thought he was 23 when he died? He died a month before his next birthday, didn't he?