Multiple Sheets All Reference The Same Column(s) To Match Data?

I've created 12 identical work sheets for the year, each has 6 columns of data and 87 rows all containing different information (letters, numbers, dates and characters).

I've also set up a "Conditional Format" rule so that any identical information triggers a strikeout (line through the cell entries) of the entire row for both lines of offending duplicating data. To do so, I created a use cell off to the side (in column AT) with the command =CONCATENATE (u41,v41,w41...) which condenses all data into 1 cell.

Afterwards, I went into Conditional Formatting and created the strikeout command with =COUNTIF($A$T$29:$A$T$116,$AT29)>1; where the $AT29 reference simply identifies the cell to the left and then continues down.

This has worked well but I'm stumped. Now I want the reference to extend to the previous month, lets say I'm in February and want to extend the search to Januarys AT29:AT116 review.

simply use a reference in the COUNTIF formula in the Conditional Formatting rule that takes the search through to the January work sheet, then I can simply duplicate the command for the March sheet which will then review all 3.