When there is an important Dvadasi, the Ekadasi fasting is transferred on the Dvadasi, and this is called Mahadvadasi. The 26th October, 1970, is actually Dvadasi, so the fasting is observed together, or Ekadasi fasting is disregarded, and the Dvadasi (Mahadvadasi) fasting is taken as important.
Letter to Pradyumna, 29 April, 1970