[tz] Issues with pre-1970 information in TZDB

[Paul Eggert]

On 9/22/21 11:31 AM, Brooks Harris via tz wrote:
> Indeed the changes would have significant consequences to my current (in 
> development) tzdb parser which reads the source files directly with no 
> modifications to accumulate all time zones that have existed.

If the goal is to accumulate all timezones that have ever existed in 
tzdb, the parser should read 'backzone', as 'backzone' has for some time 
been the repository for entries that were formerly Zones but are now 
Links in the default database.

If the parser reads 'backzone', you shouldn't notice effects due to the 
recent alike-since-1970 changes. Otherwise the parser should be changed 
to read 'backzone', regardless of whether the recent alike-since-1970 
changes are present.

Even 'backzone' won't suffice to achieve the goal I mentioned, as I 
vaguely recall some deleted Zones never made it to backzone way back 
when. I don't recall the details, unfortunately. You can get most of the 
details by looking at the Git history, I expect, but it'd be a bit of a 
job. If you find out anything from that search, please let us know, as I 
expect these old deleted Zones should be put into 'backzone' though this 
is low priority.