[tz] Adding verified historic details

Lester Caine lester at lsces.co.uk
Wed Sep 4 23:22:04 UTC 2013

Guy Harris wrote:
> What about locations that are in a single tzdb zone, so that they currently don't differ in post-standard-time, but that we discover didn't all maintain the same GMT offset subsequent to the adoption of standard time or didn't follow the same rules for "shifted time" (to avoid the term that implies that daylight is being saved and the term that implies that this shift only happens during the summer :-))?
If the system can't currently handle a fact it needs fixing so it does.
But this one is covered by the proposal below.

> And what does the adoption of standard time consist of?  Is "standard time" only specified by the actions of a government (whether national or sub-national or local), so that standard time can only be adopted by a government, or does it include some form of non-governmental standardized time (e.g., railway time) very broadly used?  For the former, we can (at least for national governments, and probably sub-national governments in many nations, and perhaps even local governments) establish a fairly firm date for the adoption; for the latter, that might be more difficult to establish, unless we simply decide to say that, once the railways agreed on standardized time, "OK, these regions are on standard time" and ignore people who weren't keeping railway time.
I already have documentary evidence for a second layer of offsets and I could 
make an argument for that, but it needs a more major change to the record 
structure to return multiple timezones so that is on my back burner.

I've listed elsewhere a couple of changes that will both save space in reusing 
existing timezones, and allow adding single events such as different start dates 
and then 'link' to the following timezone sequence. Any documented change to 
changes in time should be capable of being documented. The adoption of GMT 
related standard time is one which is fairly clear cut, but any previous local 
standard should be allowed, and LMT seems to be the norm prior to having clocks 
accurate enough to show the differences across a country so is a natural background.

>> >If there is documentary evidence of a different time pattern such has been added for the Isle of Man and is about to appear for the channel islands then it should be allowed not blocked.
> As,*for those locations*, that creates no new tzids (there were already tzids for the Isle of Man and, that's fine with me and, I suspect, Paul.
But why should what facts are allowed be restricted by some 'mistake' in the 
past? A fact is a fact ...

> If, however, we were to discover documentary evidence that, for example, some towns in New Jersey chose not to adopt daylight savings time in 1918:
> 	https://en.wikipedia.org/wiki/1918_Standard_Time_Act
> supporting*that*  in the tzdb would require splitting America/New_York and creating a new tzid or tzids for those towns.

NOT supporting a fact means that anybody who is looking for the correct historic 
data is not going to get it. If it is not going to be added to TZ then we need a 
TZ+ that does have it - end of story ... the same with every new fact that is 

We need to split the date and code to create two repositories, fork the data 
repository and then we can get on with TZ+ ...

Lester Caine - G8HFL
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