I've found a problem with the tzfiles for Africa/Cairo and America/Argentina/San_Luis. They both show a last known transition in the recent past, and surprisingly lack a POSIX-TZ-format rule for extending the zone into the future. My tzfile parser treats a zone with no extension rule as being undefined for any time following the last explicit transition, so for these two zones it reckons the zone is undefined for the present. In the source files they're each currently configured to observe a set of DST rules, and the ruleset has no transitions configured for the future. So for the present and foreseeable future, the zone is on a constant offset with no DST transitions. The tzfile reflects that by showing no transitions from the present up to 2038 (where zic always fills in a complete set of expected transitions). It should be trivial to also reflect that foreseen behaviour in a POSIX-TZ string that just gives a fixed offset and no DST rule. For example, Africa/Cairo should clearly have "EET-2". I could have a go at a zic patch to fix this, if the regular zic hackers would like to work that way. For America/Argentina/San_Luis there's an extra wrinkle: the last known transition is a transition *to* DST. Its fixed-offset foreseeable behaviour therefore has a fixed is_dst=1, which is moderately silly. It's arguable that in this case it would be incorrect to give a "WARST3" extension rule, because that doesn't accurately express the DST status. Since that DST transition was in 2009, it's also a good bet that they haven't stayed continuously on DST since then, of course. -zefram