"Trevor Talbot" <quension@gmail.com> writes:
> I don't know if there have ever been retroactive changes to DST laws
> we could look at, but I could easily see a change like that affecting
> some things and not others.
Even a politician would hardly be silly enough to make a retroactive
DST law change. On the other hand, it is *entirely* possible for a
computer system's DST rule files to be updated only after the effective
date of a law, and I think that's the case you'd want to design for.
Maybe, when you look at it that way, the past and future cases aren't so
different after all ...
regards, tom lane