Interesting! I definitely do not get the impression from the author or her website that they're intended as YA. Laurence as a protagonist in particular argues against it to me--he's not just an adult, he's firmly an adult--about 30 in the first book. If he had started out a lieutenant in his early twenties, I might be able to read the books as YA.

The lines between YA and A are awfully fuzzy, and a lot of A is perfectly reasonable for teenagers, so I'm not sure it really matters that much.