When I enter either COUNTIF(A:A,">0") or COUNTIF(A:A,">1/1/1900") into the cell, change the "A"s to "M"s, and then press Enter, I don't get a number in the cell, I get "COUNTIF(M:M,">0")" or COUNTIF(M:M,">1/1/1900").

And I haven't tried the longer formula

>>In cell B1:

=(A1>=$C$1)*(A1<=$D$1)*(CELL("format";A1)="D1")
copied down to B10 and then =SUM(B1:B10) where C1 is the earliest allowed date and D1 the latest allowed date...<<

because I would have to change D1 in 2 places of the formula every time I entered a new date in the cell (unless I'm misunderstanding something)...