As far as I'm aware, we don't maintain any archive of old Fenix Nightly or GeckoView Example App (gve) builds, beyond the ones that TaskCluster maintains for 1 year.

As a result, if you're testing a regression that you suspect to be introduced more than a year ago, then mozregression will tell you that it can't help you, like so (emphasis added to show the oldest build that we've currently got available):

$ mozregression -n gve --good 2019-01-0
[...SNIP...]
INFO: TaskCluster only keeps builds for one year. Using 2020-10-14 13:15:13.701889 instead of 2019-01-01.

Could we set up some sort of archive for daily[1] builds, for fenix and/or geckoview example app, so that we can usefully test for regressions that were introduced more than a year back? (whether via mozregression or manual apk-installation)

[1] Or weekly, or whatever cadence we can do (e.g. exponential decay), if daily builds end up requiring too much storage space.

In late 2021, we started to upload Fenix builds to archive.mozilla.org which should make them available to mozregression. I'm closing this bug as a duplicate but feel free to reopen it if this doesn't work as expected.