In plain English, for the versions BubbaDog and I posted, it’s going:
If there is anything at all in A1, assign the value “1” as the answer to this question. If there isn’t anything there, assign the value “0” as the answer to this question.
If the month in A1 is 11, assign the value “1” to this question. If the month isn’t 11, assign the value “0” to this question.
Now, multiply the answers from Question 1 and Question 2 together.
Now do this for A2 and so on, all the way down to the last cell mentioned.
THEN add the results from each row together.
So for any given row, if the answer to either question is “0”, then the result of the multiplication will be zero. You’ll only get a “1” if both questions are answered positively. So the final result will be only those cells where there is something there AND the month is 11. Then they all get added up and bada bing, all Novembers are counted. (A pivot table will do the same thing much more quickly and easily but as has been pointed out, it has several drawbacks.)
In later versions of the formula in this thread they’re able to dispense with the first question altogether by assuming that there will definitely be something in each cell to look at.