From what I feel it is the way the depots deal with their
fleets.
852's case was because of wrong fleets deployed and getting
messier, which resulted in AMDEP taking 5 duties back. 859's case I
don't see the need as the fleet is tidy enough, 106 I can close 1
eyes, 171 is steady enough.
In return AMDEP transfer 4 of 980's duties back to WLDEP.
Those former Nissan UD perms from 852 were then thrown over to
178 instead.
I still remember spam Nissan UDs being deployed on 852 by WLDEP,
which was a sudden nightmare.