I suppose you are trying to the discover if it is possible (but not necessary) to figure out the amounts of alcohol consumed before and after the accident.
Blood alcohol level alone won’t do it. But it is possible if that test is combined with liver enzyme test for ADH and ALDH, and a complete urinalysis
It takes the liver time to breakdown alcohol. If the alcohol was consumed hours before you could expect to see more of one enzyme than if the person was tested right after consuming. Since every person is different you would need to do follow up control work to determine that person’s specific metabolism and alcohol breakdown rate.
Also, if you know, or have a sample of, the alcohol consumed both times you might be able to get additional verification from the flavoing and coloring products added to the drinks.
Science was able to determine what Otzi the Iceman ate 5000 years ago. They can figure out how much alcohol was consumed and when, if they are willing to spend the time, money, and resources.