Formula references - Referencing other tabs through auto lookups

[EH123]

Hello

Happy New Year everyone :-)


I have a workbook which needs to refer to a different tab each month. For example, last month, my formulas looked like this;

e.g. =COUNTIFS(INDIRECT($A4&C$1),$B4,'Nov20'!$CT:$CT,1,'Nov20'!$CU:$CU,1,'Nov20'!CV:CV,1)

I now need all to reference 'Dec20' rather than 'Nov 20' (there's a lot of different formulas and will take ages to manually change from 'Nov20' to 'Dec20', as well as possible human error in missing one).



I have made a look up table for it to refer to (e.g.you can see I've tried various different ways to reference it!).

SELECTION = data validation of the first column below. then columns 2, 3 or 4 pull through

Apr-20 "Apr20"
May-20 "May20"
Jun-20 "Jun20"
Jul-20 "Jul20"
Aug-20 "Aug20"
Sep-20 "sep20" Sep20 Sep20!
Oct-20 "Oct20" Oct20 Oct20!
Nov-20 "Nov20" Nov20 Nov20!
Dec-20 "Dec20" Dec20 Dec20!
Jan-21 "Jan21" Jan21 Jan21!
Feb-21 "Feb21" Feb21 Feb21!
Mar-21 "Mar21" Mar21 Mar21!


I've tried referencing it to the lookup in columns 2, 3 and 4 but I keep getting errors saying there is a problem with the formula.

Any help much appreciated!

Thanks
Emma