The L on the serial number and in the round seal corrosponds with the 12 (it is the 12th letter of the alphabet).
If you read the black seal that surrounds the large L you'll see that it says "San Francisco".
This seal with the district has been removed from the redesigned bills.
As far as I know the G at the end of the serial number is just part of the sequence. After they get through E, then they go to F, then they go to G.
I don't know if they start with A00000000A, but I do know that they have a 00000001.
I've heard that they usually pull the first 300 or so bills out of run so that they can sell them at a profit. So its hard to find a bill lower than 00000300.
I picked this bill out of circulation in the late 80's.
Image:
cool_bills_00000001_avatar.jpg3.63 KB