Doreish Haemes: Lamed nissan can never be on shabbos based on the dictum of LO ADU ROSH. For Lamed Nissan to be on shabbos, alef nissan would have to be on Friday which means Alef Tishrei would fall on a Sunday, which cannot happen on our calendar. See Orech Chayim Taf Chaf Ches Siifim Alef and Beis for the days Rosh Chodesh can fall out along with MB Sif Koton gimmel.
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