I think you just blew up 'open theism'
I want to agree, God knows all things at all times - even things which are not. It stands to reason that He paid the price for all sin He knows. So His sacrifice atoned for even sins that might have been but were not - and its more than 'covering' sins with His blood, like the blood of the sacrifices in the law; He removes sin. If He removes sin in its entirety, He removes even what sins were never actualized.