Thanks for all that careful work. I installed the attached patches,
which implement the changes you suggested, except that they retain
2022f's guess that Yukon's 1965-04-22 spring forward was 00:00→02:00
instead of 02:00→04:00 as the former seems a bit more likely to me
(admittedly this is just a guess either way).

Also, I looked for other evidence about Pangnirtung and found a Google
Books snippet suggesting that EST was used in 1959, so these patches
move America/Pangnirtung's data to 'backzone' since it appears there's
no difference from America/Iqaluit since 1970. There is a
backward-compatibility link as usual.