Counting seems to be going out of fashion. Federer has not played 21 tournaments in the past 12 months. This year he has played 12, as you can see from the fact that he has lost 6 tournament matches, won 5 tournaments and withdrawn from 1. Last year from this point on he played Cincinnatti, US Open, Basel, Paris and WTF. So 17 tournaments is correct, or 18 if you count DC.
maybe ATP should learn to count then?