Well, actually there are a few more. Here is the full list:
BT.15
CL.09
CL.13
KH.16
PH.B2
PH.C8
PH.E1
RU.90
Also there are 'undefined', 'null', '00' and '' (empty string) as admin1 codes.
Instead of having different things, is it possible to make them standard such that '00' or '' to denote an unknown state ?