Dynamic indirect reference with named lists

Hi experts,

I am trying to sum over multiple sheets dependent on multiple criteria.
I reproduce below the formula in one of the cells which is summing certain cells on sheets dependent on whether the sheet is on a named list.
So in the below example and attachment, any sheet defined as “Merchant” and matching the account description in cell a12, the value contained in cell a12 of any sheets defined as ‘Merchant’ will be returned. Therefore, the value 76,490 is returned from sheets ‘MPA4T’ and ‘MPAPP’ as both are on the named list.

=SUMPRODUCT(SUMIF(INDIRECT("'"&Merchant&"'!"&CELL("address",$A12)),$A12,INDIRECT(Merchant&"!"&CELL("address",$P12))))


This is all working fine. However I am struggling to make the ‘Merchant’ bit dynamic. Thus I want to insert a cell reference so that when I copy across I am not having to hard code to ‘King’ etc… Please help.

Sbz