[tz] Fwd: [IANA #1283803] Europe/Amsterdam

[Paul Eggert]

On 10/17/23 04:08, Leo Bekhuis via tz wrote:
> *Is Europe/Amsterdam currently an IANA compliant timezone?*

"An IANA compliant timezone" is not a well-defined concept. As 
<https://data.iana.org/time-zones/tz-link.html> says, the tz code and 
data are by no means authoritative. (Brian discussed this in more detail 
in his reply.)

Possibly you are asking about timestamps before the year 1970? Although 
TZDB's scope is timestamps since 1970, because of its formats it also 
covers pre-1970 timestamps in limited ways. In the latest TZDB release 
(2023c) with the default settings, Europe/Amsterdam is a Link to 
Europe/Brussels so their timestamps are identical. However, if you use 
some non-default options when building from 2023c, Europe/Amsterdam 
becomes a separate Zone with data that differ from Europe/Brussels for 
some pre-1970 timestamps; although this optional Zone is also incorrect 
for some pre-1970 timestamps, it's closer to being right. The 
non-default options exist for compatibility with older verions of TZDB 
that were more ambitious (arguably too ambitious) in their attempt to 
cover pre-1970 timestamps.

One other thing: downstream distributions commonly tailor TZDB for their 
own needs. Often there's no combination of options for the 
IANA-distributed TZDB that will generate timestamps that exactly match 
what you observe on your own system. So one must be careful about 
phrases like "IANA compliant timezone". If you want 100% reproducible 
timestamps, you'll need to give more detail about how you derived the 
timestamps.