I know some of the letters were published in the newspaper during Albert's lifetime -- he was just that famous.
The first biography came out right after his death. The author visited Albert in late 1917 for interviews for the book (which Albert was very embarrassed about) and used some of the letters then for combat details and more letters were made available by his parents after his death. Like I said, the letters are very schoolboyish, there was nothing embarrassing in them. The ones I've read of a more personal nature dealing with girlfriends and other things you wouldn't exactly broadcast are in the archives.
I've been encouraged to write a book because I have turned up some new information, but I still think there is more out there to be discovered.

h34r:
Cheers,
Scarlett