Well, here is something to think about...
When the 2002 Changeover happened from one printer to the other, it ended at AOF. Now, what if....
There might have been AOG back then that may have never been released. So they can not re-use AOG now, so they went straight to AOH now. :-/
As for HPB... The fact we have only found 7.5 and under HPA it does not look good (But NOT impossible).
The Best thing is for someone to see what the BoC Museum has for their "First 3 Notes" of the 2006 Notes (AOG or AOH). Best way to tell at this point.
Brent, i think you have good connections to find this information out...