On Sep 22, 2021, at 3:23 PM, Howard Hinnant <howard.hinnant@gmail.com> wrote:
On Sep 22, 2021, at 5:17 PM, Tom Lane via tz <tz@iana.org> wrote:
One thing that's particularly sticking in my craw about the changes under debate is that they undeniably made tzdb worse as a description of reality in the places at issue.
This is my objection as well. Before the change the tzdb does a “best effort” on pre-1970 dates.
"Best" in what sense? The 2021a data makes an effort to keep the data for Europe/Oslo separate from the data for Europe/Berlin. It makes no effort to keep the data for America/Montreal separate from the data for America/Toronto. The comment in backzone about the America/Montreal data is # Canada # # From Paul Eggert (2015-03-24): # Since 1970 most of Quebec has been like Toronto; see # America/Toronto. However, earlier versions of the tz database # mistakenly relied on data from Shanks & Pottenger saying that Quebec # differed from Ontario after 1970, and the following rules and zone # were created for most of Quebec from the incorrect Shanks & # Pottenger data. The post-1970 entries have been corrected, but the # pre-1970 entries are unchecked and probably have errors. # The comment in the 2021a europe about the Europe/Oslo data is # Norway # http://met.no/met/met_lex/q_u/sommertid.html (2004-01) agrees with Shanks & # Pottenger. so the difference here appears to be how well-vetted the pre-1970 data is vetted. So does "best effort" mean "provide pre-1970 data in the default configuration if we have reason to believe it's accurate, but provide it only in backzone if we don't"?