I'm facing this problem.
I have around 70 products in different categories and different attributes sets, but with the same common attribute (SKU). I have 3 catalog price rules which applies different discounts. I want to exclude products by SKU from this discount rules. I have used this method and also Is not:
The problem with this method is that it's doing something weird, it excludes the specific sku from the discount succesfully, however other different products are being excluded from the discount rules too. The products that are being excluded are not from the same category or attribute set, I don't know if that is the cause.
I need to keep the discount to all products except for the ones that I will exclude on the discount rules.