RPOL's birthday?
For a long time we didn't record signup dates, so anything prior to.. errr, some date I can't remember are really rough estimates (e.g. "Before 08:00, Sun 23 Oct 2005", "Before 10:53, Sat 05 May 2007") which I only managed to get by dumping old backup copies of the user database and getting a list of who was in it.
Anyone after ~May 2007 have proper accurate signup dates, but the first 42,000 or so users only have the aforementioned rough estimates.
So I can let people see their signup dates, but if your account number is under 42 thousand and something then you'll only get an estimate.