When they reach Girijanath Temple they remove old pole and the new pole is kept. And the old one is kept with the old ones. If we count those poles before keeping the pole they are 21 and after keeping the pole they are 21.
Upon reaching the Girijanath Temple, they discard the old pole and retain the newly installed one. The discarded pole is then added to a collection of other old poles. If we count the poles before removing the old pole, there are 21. After keeping the new pole, there are still 21.