Not only that they would have either been using it consistently since they learned it or just learned it. I at one point could do differential equations (linear alg + calc). If you put one of the remedial problems in front of me I would not be able to do it. That info is just 'gone' from 25 years ago. But obviously I can do it. I got an A. I know enough right now to know what to go lookup so I could re-learn it if I needed to.