[tz] Issues with pre-1970 information in TZDB

Paul Eggert eggert at cs.ucla.edu
Thu Sep 23 17:22:35 UTC 2021

On 9/23/21 7:32 AM, Tom Lane via tz wrote:
> That's half of the issue.  The other half is "if a zone does not contain
> relevant pre-1970 data, how would end users know that?"

For most users the answer is simple: the pre-1970 data should not be 
relied upon for anything other than an estimate. That data are intended 
only for exact locations named, and most people in the world do not live 
in those exact locations.

For example, Europe/Berlin is wrong for most of Germany before 1970. 
Similarly for Europe/Rome and Italy, Asia/Shanghai and China, etc., etc. 

None of the pre-1970 data should be used for anything important, at 
least not without understanding its severe limitations.

Luckily for us, tzdb users invariably follow the advice I'm giving here, 
whether consciously or not.

More information about the tz mailing list