Chris,
Two different things here - one was a bug, the other is a feature that
did not exist yet. Both are fixed now, in v4.2.7, published today.
The null owner: when a member is permanently removed from the roster
(the wastebasket purge action), anything that still pointed at them
should have updated, and one thing didn't. A vehicle they were marked as
owning kept a reference to them even after they were gone, so the owner
column had nothing to resolve and showed blank with nothing to explain
why. That's fixed - purging a member now clears them from any vehicle
they owned.
The Agency question: you can now actually do this. Editing a vehicle,
the Owner field is a three-way choice - Person, Agency, or none. Pick
Agency and you get a dropdown of your existing organizations (the same
list under Settings > Organizations) - no new setup needed, it reuses
what you already have. An agency-owned vehicle you had already marked
with the old "Agency Vehicle" checkbox will open showing Agency selected
with nothing chosen yet - pick the right one and save, nothing else to
migrate.
git pull and it is all there.
Eric