[tz] Issues with pre-1970 information in TZDB

[Steve Summit]

Guy Harris wrote:
> What if [the pre-1970] data 1) has been determined to be correct based on
> sources we deem sufficiently reliable and 2) it applies to more than just
> the city and its environs, but it doesn't apply to, for example, the entire
> country?  Should one or more new tzdb regions be created for those other
> locations?

I'm starting to feel like I'm dealing with Vroomfondel and Majikthise
here, demanding rigidly-defined areas of doubt and uncertainty. :-)

In all seriousness, I think we need to take some of the energy we're
expending on the pre-1970 database correctness problem, and redirect
it towards exhorting end users *not* to depend on pre-1970 data too
much.  In particular, if there are people out there who are taking
pre-1970 local timestamps, using tzdb to compute proleptic Unix
time_t values, and storing those timestamps in databases, such that
changes to tzdb will later cause interestingly-wrong local timestamps
to pop back out, we need to get the word out that this may not be the
best way of doing things, after all!