Why is a product's discount greater than what is set in the Max discount field on the product?

Warning and the option of removal on products that doesn't meet the discount percentage criteria can easily be done.

If a product that you have set a maximum discount percentage on in Products (PIM)>Products still appears in a campaign, it may be because you forgot to remove the product when setting up the campaign. A warning will appear indicating that the product exceeds the set percentage for the campaign. If no action is taken, the product will still appear in the campaign. You can easily review or remove products from the selection, or adjust the specific product to the correct maximum percentage in the Discount(%) column. You have the option to remove all products at once or remove them individually. An exclamation mark (!) indicates that a product does not meet the criteria.