Even though the rule currently in effect now is identical to a neighboring some, that doesn't invalidate the first zone. The main reason is for scheduling purposes where, going back in the past for example, the difference is now a matter of historical record and needs to be kept for software that care for such things such as calendars.

For example, if your are in Argentina/San_Juan and your calendar has a meeting in the past (for legal reasons you are keeping track of your meetings) where the zones were different, the rule is still in force. Were the Argentina/San_Juan removed that meeting time would then move by 1h when applying Argentina/Buenos Aires in place.

This is more obvious if you have a meeting where some attendees were in Argentina/Buenos Aires and some were Argentina/San_Juan. In that case, with the old timezone the meeting (say a conference call) occured at two different wall clock hours with the old rule (as it actually happened at the time) vs with the Argentina/Buenos Aires rule in place forces both meeting to have not occured at the same wall clock hours. The UTC never changed, just the wallclock but that's what we need the tzid to get right. If the meeting occured around midnight, it could even change day for some attendees!

So to maintain historical accuracy the old rule cannot be taken out.

On 23/01/2014 5:40 AM, Fabiano Fidêncio wrote: