rabbiofberlin,
I looked up the rule of ???? ????? ????? ????. It very much seems the exception rather than the rule.
I found an interesting ??? ??? in ?”? ??’ ?”?, who asks why we need the rule of ???? ????? ????? ???? when we have a universal rule of ?????? ??? ??? ????? (according to most ??????, even the first day of ????? is ?????). He answers that since ????? is often at the expense of other ?????, such as ???? ??? or ???? ???, the normal rule of ?????? ???? ???? ???? does not apply; similar to the idea of ??? ????? ????.