[_djo_]

You're right about international flights and I should have specified that, but you can view the aircraft's recent US-only flights and see that it also used its permanent ICAO code.

[leereeves]

There are also gaps in the history ("no data available") of the permanent code, like:

https://globe.adsbexchange.com/?icao=a835af&lat=34.765&lon=-...

Couldn't they have used the PIA code on those days?