One possible reason is because AMDEP loses control of several
services' slots. Losing 6 slots of 171, 12 slots of 852 and 7 slots
of 859, they only gain back 4 slots of 106, 8 slots of 985 and
3 slots of 190. Overall they have a loss of 10 slots, and so they
would have to transfer some rigids over to supplement the other
depots handling these extra slots.
AMDEP was clever enough to transfer some UDs though. =D
9 slots for AMDEP 985 to be exact.
Those 3 Nissan UDs that AMDEP transferred to
KJDEP (CSS184S, CSS189D, CSS194M), are now service 975 new
permers. 
In fact AMDEP had gained 10 slots/buses earlier this year from
WLDEP, when service 961 came under partial WLDEP/AMDEP.
So now it's pay back time 
