They aren't going to check the date on the receipt. They are Wal-Mart greeters, for god sake.
But seriously, though, I never tried this, nor claimed to have tried it, it's just a crazy plan I thought up, and I really don't recommend doing it unless you REALLY know what you are doing. It could very well work if executed properly, but the more you steal at one time, the more likely you are to get caught. Small amounts are always going missing from Wal-Mart all the time, but Wal-Mart is making such high profits that it doesn't even matter. It's the big inventory losses that Wal-Mart is concerned with, like $3,000 worth of shit disappearing in one day. For this reason, it's much wiser to take small amounts randomly.
For example, don't go to a store for the sole purpose of stealing. Just steal a little whenever you happen to be shopping. For example, if you are buying clothes, put on a few extra shirts underneath your hoodie in the fitting room. Whenever you go grocery shopping, eat food off the shelf. Put an fancy watch or some jewelry in your big gulp every once in while. Be creative.