The walgreens system is computerized and will not let you sell the product if it is over the daily or monthly limit and the data is readily retrieveable.
That's what someone left as a comment to the last post. If that's true, then I have a bone to pick with the Walgreen's pharmacist down the street from us who told me he had no way to find a specific person's history in their electronic database. If it turns out that it's readily available, then he was being lazy (and that's not even a busy store), and I'll be calling him back soon.
Is it possible that it could differ from state to state? It doesn't make much sense, but I'm completely oblivious to other state's laws.