Shops rarely if ever change the shelf edge labels when they are forced to give products away for free, under their own offer, when the shelf edge label differs from the price charged at the till.
So you could have gone back into Superquinn, and bought loads of the baby formula, and then got it all for free. Check out the offer carefully first, and keep in mind you must pay for the products and then ask for a refund. Although they won't be happy, and they may refuse to pay,.. the fact that they make no effort to change the shelf edge labels when they know they are wrong means they are leaving this possibility open.
The problem is that the till operator may become suspicious, and refuse to charge you.