[tz] Merged 1970+ time zones should always return -1 pre-1970

Paul Eggert eggert at cs.ucla.edu
Wed Sep 29 19:58:32 UTC 2021

On 9/29/21 12:06 PM, Robert Elz wrote:

>    | That particular data entry must be wrong,
> Sorry, "must be" is not an argument that has any traction with
> me at all, no matter what the issue.

That's not a viable standard. By that standard, someone could invent 
some data saying that Bamako was 4 hours ahead of GMT in 1938 and then 
say "prove me wrong". We shouldn't include data in tzdb merely because 
we can't (or lack the time to) prove it wrong.

Here, the only evidence we have is Shanks, and Shanks has been shown to 
be wrong so often that it's almost *negative* evidence. Shanks often 
invented data for older timestamps that are harder to verify. He did it 
over and over again. Shanks's pre-1970 data is terrible data and we 
should rely on it as little as possible.

Since you insist on questioning my admittedly uninformed suspicion of 
that particular data entry, I did a bit of legwork for it. That data 
entry comes from the Shanks & Pottenger International Atlas, 6th edition 
(2003), page 257 (Mali, Time Table # 1, and column 1 of the main data), 
which says that Bamako observed -01 from 1934-02-26 00:00 to 1960-06-20 
00:00. However, 1959 American Nautical Almanac (published in 1957 in 
London by Her Majesty's Stationery Office and in Washington by the US 
Naval Observatory), the "STANDARD TIMES (Corrected to December 1956)" 
table, List II, page 264, says that French Sudan (which at the time 
existed and contained Bamako) observed G.M.T.

Neither of these are primary sources, of course. That being said, of the 
two sources, the American Nautical Almanac (though often flawed) is 
typically more reliable than Shanks. At least some of that Shanks data 
item is most likely wrong.

This is just one data item, and from the information given above it's 
not clear how to fix it. Nor do we have time to fix it. Nor do I want to 
  (or have the time to) go through a similar exercise for all the other 
data items for Bamako (also quite possibly wrong) or for all the other 
data in 'backward' (also a lot of it wrong). But that's OK since this is 
just low-quality pre-1970 data in 'backward', and nobody (I hope) relies 
on 'backward' for anything important.

> Eliminating abbreviations is another task that's been undertaken with
> some abandon

I eliminated only abbreviations that I had earlier invented with abandon 
and so were unsourced. 'HST' is a widely accepted English-language time 
zone abbreviation, which is why I didn't eliminate it.

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