There's always a ship start and a ship end date, which you can check in the stickies in the Customer Service forum. Your order can ship any time in that window, and when it does you'll have access to the pdfs. So some people will get them on the 15th, and some people not until the next week. (Note: On Thursday the 11th, the order will spawn. This is not your shipping notification, just a notice that your order has processed. You'll get another email when it ships.)
I'm new to the buying them as they release. When you say ship to subscribers the 15th, does that mean they are also available to download on the 15th, or is the street date of Aug 31 for the download as well?