These plates seem to be issued to city government vehicles that do not fall into other categories: People Mover buses, city police, utility trucks owned by municipalities, etc.
The current XX- series begins with XXG.
Missing: [XXH], [XXK], [XXR], [XXw], [XXZ]
I suspect that the reason that the AST on these plates is suffixed rather than prefixed is to avoid a collision with AST-prefixed plates from the '76-'77 bear-plate run.
Special thanks to the Alaska State Troopers in Palmer for letting me take these pictures.
Norm Ratcliff (ALPCA #3677) has a great page about the history of Alaska State Trooper plates.
Thanks to the Fish & Wildlife Protection office in Palmer for putting up with me (briefly) while I took these pictures.
Missing: [FWP] (suffix)
Plate #1 is the Governor's, Plate #2 is the Lieutenant Governor's, and 3-63 are assigned to the State Legislators, apparently assigned by seniority rather than by a legislator number or district number.
I have seen a couple of the Centennial plates with the prefix LEG and a two-digit number (sometimes centered, sometimes not):
I'm pretty sure that most people can't get a plate with a number lower than 63 in it, so I'm not sure why some of the plates above appears to be personalized plate rather than legislator plates, but I'm pretty sure that they're the latter.
There are also specialized Centennial plates for Alaska State Senate and Alaska State House, though I've only seen a few of them. Note that the State Senate plate has the embossed numbers while the State House plate has the printed-on, thinner-font numbers:
It is legal for a state legislator to display legislator plates on more than one vehicle. Dirk Starck reports that he's seen them range from three to five pairs.
From AS 28.10.181:
(f) Vehicles owned by elected state officials. The department shall issue special registration plates to each incumbent elected state official for display on noncommercial motor vehicles owned and driven by the official. The department shall number or design the plates so that registration by an elected state official is indicated upon the plates. The registration plates issued under this subsection remain with the owner of the vehicle only during the official's term of office.
I have seen plates as high as 99---, but don't have any examples yet.
There are also some U.S. Government and related plates.