MacRumors renderings, by Ferry Passchier, of the alleged 4.7-inch and 5.7-inch sixth generation iPhone lineup. Photo used with permission.

So you've heard all the rumors of Apple's (NASDAQ:AAPL) next iPhone release. The iPhone 6 is supposed to be bigger, faster, and packed to the gills with exciting new features. Chances are, it will even have panes of sapphire crystal covering the touchscreen, tossing the scratch-prone old Corning (NYSE:GLW) Gorilla Glass aside.

But it's all been rumors so far. Rumor are Apple is working up a new design and previous iPhone releases have arrived in the late summer, early fall season ever since the iPhone 4S went on sale in October 2011. This trend would align with the rumor mill saying that the next version should arrive in September. But how will we know that the (not-yet-officially named) iPhone 6 will meet that schedule?

Here's how: Wal-Mart (NYSE:WMT) just put last year's iPhone models in the bargain bin. You can walk down to your local Supercenter today and pick up an iPhone 5S for $99 (with a two-year carrier contract) or an iPhone 5C for $29. That's a $50 discount on iPhone 5S and $20 off the 5C model.

These discounts happen every year, usually right around late June. Wal-Mart needs to clear its inventory of unsold handsets to make room for Apple's latest and greatest devices, and this year is no different.

How consistent is this purported iPhone predictor? I'm glad you asked:

  • On June 22, 2013, Wal-Mart hacked $60 off the price of iPhone 5 handsets and $50 off of the aging iPhone 4S.

  • 2012 was the exception to prove the rule. A $74 Wal-Mart discount on iPhone 4S showed up on May 4, but was then canceled and said to be a "pricing error."

  • For almost the entire month of June 2011, some Wal-Mart and Sam's Club stores cut $52 off the iPhone 4 price tag.

  • Wal-Mart got started early in 2010, offering a huge $103 discount on iPhone 3GS as early as May 25. Then again, this was back when Apple announced its next-generation products very early, and the iPhone 4 was on store shelves before the end of June.

So if you were worried about Apple's release schedule slipping for any reason, Wal-Mart basically just told you to relax. The retail giant would not take this action unless it knew what Apple will send over to replace the old 5S and 5C inventories and when, not to mention at what cost.

Chinese supply chain rumors are fun and all, but I really wish I could be a fly on the wall in Wal-Mart's Bentonville operating hub. These guys are in the know before we even knew there was something to talk about.

Some observers have worried about limited sapphire supply potentially pushing this release back by several months. Others saw possible delays in the supposed top-to-bottom design change, which will reportedly be a big change from the incremental improvements of the last few generations. Or that new product lines like the long-rumored iWatch would distract Apple from delivering iPhone 6 on time.

But the clockwork-like punctuality of this year's Wal-Mart price cut is a solid sign that Apple has its ducks in a row once again.

But what else did you expect? CEO Tim Cook was always an operations and supply chain specialist, after all. Wal-Mart is simply proving Cook's rock-steady execution powers one more time.