When the stores unload trucks the mechandise that can't fit on the sales shelves goes up high throughout the store. Most people think of a store's storage area as "the back room" when it's really just up high through the store.
A lot of times the store's inventory will show that they have some in stock, but the sales shelf is empty. It usually means it's in top stock, somewhere. It varies by store, but there doesn't seem to be much if any tracking on exactly where things are. The teams that put the stuff up there don't need to find it later, so they put things where it's easy, not where it makes sense. There have been items I needed to get that day, and it typically ends with me walking aisle by aisle with an employee trying to find the stuff on the top shelf.
Big things are easy, like a cabinet or water heater. But smaller items fall into cracks that are hard to see, get moved, stolen, hidden by scummy deal-seeking customers waiting for further mark downs, etc. Those are the things that you'll have a tough time finding.
