I have watched this happen. Pricing team comes through, raises everything a few cents, then it goes on sale a week later. I worked in retail, mostly food, food usually only goes up a few cents. The sale usually made the price lower, even before the raise, but the retailer was still able to grab a few extra pennies.
Black Friday is a prime example of not having sale items in stock or a limited amount. But available stock also has to do with the volume and location of the store. If you are in a small area, that particular store might only receive a few of the items or none it all. A larger volume store will receive the bulk of sale items. If the item wasn't on the truck, before the sale, it will not be on a later truck. Yes, we did say "Sorry, our shipment didn't come in today. We will be getting another tomorrow." Most of the really hot deals were not available online either.
The only way to get a good deal is to shop the clearance sections.