Assume three validly outstanding make-up fasts and an effective bequest. Using wheat, three daily half-ṣāʿ allowances yield one and a half ṣāʿ of wheat in total.
Using any named one-ṣāʿ-per-day foodstuff yields three ṣāʿ in total. This is only the arithmetic of the food measure; validity of the bequest and available estate assets remain separate legal questions.