One friend could tell the difference between the Coke made in Toronto vs made in London, Ontario. He much preferred the latter, maybe something to do with the water. Whenever he heard anyone was going to London he would try to get them to bring some back paying for the trouble. We put it to the test, he correctly guessed a handful of times in a blind test. Then we mixed them, he said "you mixed them."
Could there be a significant cohort of people who are unaware they have a diminished sense of taste due to age or other factors?