[tz] Future support for more reliable pre-1970 data

Lester Caine lester at lsces.co.uk
Sat Sep 21 09:31:22 UTC 2013

Alan Barrett wrote:
>> So the only SAFE way to distribute a sub-set of TZ data is not to link it to
>> past history that it is not 100% related to. The only problem remaining is how
>> to allow a correct historic record to be used with the restricted TZ data.
> I can't parse that, but I suspect that it's a conclusion based on a premise that
> I don't accept.

If the 'stock' distribution of TZ provides history for only ONE of the branches 
that end in a current timezone 'name' then for all other branches it is simply 
wrong? How do you know which 'timezone' the history actually belongs to and more 
important, how do you get the correct history? This is the current sticking 
point as I see it at the moment. It only makes sense to distribute data in the 
'stock' distribution back as far as 1970 and return 'not supported' for previous 
dates since there is no simple way to identify what is valid prior to 1970 for a 
particular location?

I'm in the lucky position that I can ensure that europe/isleofman and the other 
UK zones have valid historic data, but once I move to europe during the 20th 
century the results returned by TZ are more likely simply to be wrong? Therefore 
it does not make sense to return anything prior to 1970?

Lester Caine - G8HFL
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