Update on my previous post:
It seems that on-line stores can and do ship early.
Menshi confirmed that his order (with a release date of 24th Aug) shipped out a week early from AnimeCornerStore. And I can also coincidently offer a similar occurrence from DVD Pacific, I had pre-ordered an item over the weekend (which also had a release date of 24th Aug) and it was shipped out on the Mon 16th Aug.
I note that DVD Pacific still have the DVD listed as "PreOrder" with a release date of 24/08/2004, so maybe it has something to do with the fact they can't (or maybe shouldn't) advertise earlier release dates (even if they have it in stock).
So, the bottom line - It seems if you "Pre Order" a DVD, it may be shipped out earlier than the release date (in the above two examples, a week earlier). While this may be obvious to many of you who have made such orders before, I must admit that I rarely pre-ordered but just waited until the release date before making an order. Most of the time I ordered 3 DVDs at a time so I always waited until they were all marked as "In Stock" before placing an order.
I shall have to try pre-ordering Azumanga V4 and see if it also gets shipped before the 31st Aug release date