Whole Foods whittled down the list of items that are "never" out-of-stock. Now that tier of redundancy is reserved for a select group of core items explicitly called "never-outs." In doing so, HQ implicitly reclassified the remainder of the inventory as "sometimes-outs."

Having a lot of "sometimes-out" items predictably will lead to "sometimes-all-out-at-the-same-time" categories and "some-stores-are-always-out" items. The outages are clumping, in terms of categories, timing, and location. Which is a bad and apparently unanticipated mode of failure for the procurement system.