Saw the following question from R’ Yehoshua Menachem Ehrenberg (Dvar Yehoshua):
The S.A. paskens that if someone is in doubt whether he counted sefirah on a previous night he can continue counting the current night with a bracha.
The logic is that there is a sfeik sfeika in the person’s favor: 1) maybe he really didn’t miss counting the previous night; 2) even if he did miss, maybe the halacha follows the view that each night is its own mitzvah.
The S.A. also paskens that if someone asks you during bein ha’shemashos what night it is, you should say “Last night was X” because if you say what tonight it, you won’t be able to count with a bracha. Since sefirah may only be derabbanan, and when it comes to mitzvos derabbanan kavanah to fulfill the mitzvah may not be necessary, therefore just by telling your friend what night it is you may have already been yotzei.
Why in this case, where you told a friend what night it is during bein ha’shemashos, do we not invoke sfeik sfeika in your favor to allow you to say the bracha: 1) safeik whether bein ha’shemashos is really day; 2) even if bein hashemashos is night, maybe mitzvos derabbanan do require kavanah and your count was meaningless?
What’s the difference between these two cases?