defining in Frequency a changing number of rows

Hi
I would want to check the frequencey of an array that is on another sheet (here called values) . The array have different number of rows on different occasions, e.g. this week would have 14 valid rows and next week 30 valid rows. Here is an example for the 14 rows, rows 2 to 15.
=FREQUENCY(values!$AC$2:$AC$15;$A$4:$A$17)/ROWS(values!$AC$2:$AC$15)

I have a lot of tables with this kind of array taking content from different columns (e.g. AC column, AE, AK, AP, AS, AT, AX-column etc) in the values-sheet, but all columns have each week the same amount of valid rows.

To avoid updating all the frequency formulas everytime there is more or less valid rows, I would like to define the number of valid rows somewhere once and then use that definition is all the tables.

How can this be done?

Thanks for the help in advance!