sa is substituted for saha when it has the sense of 'up to the end'.,
Thus सकलं = कलान्तं ज्योतिषमधीते ॥ So also समुहूर्तम् = (मुहूर्तान्तम्) ॥ स संग्रह (= संग्रहान्तम्) व्याकरणमधीते ॥ These are all Avyayibhava compounds by अन्तवचने 2.1.6. Therefore, when a word, denoting time, is the second member, सह would not be changed to स, because of the prohibition in 6.3.81. The present sutra removes that prohibition by anticipation, with regard to time-denoting words even, when the meaning is that 'of the end of a book'. When the sense is that of 'more', we have सद्रोणाखारी, समाषः कार्षापणः सकाकिणीको माषः ॥,