I'm struggling to wrap my head around the formula in combining Index/Match and summarizing the number found across multiple worksheets.

I can dummy up a sample file later tonight, but in general.

I have ~ 50 worksheets all with a range of D12: T49

and I have this formula correctly working to pull the value from a particular worksheet, where the worksheet name is identified in cell C1 and the index/match does its thing with multi match on both the row and column.

=INDEX(INDIRECT("'"&$C$1&"'!D12:T49"),MATCH(1,(INDIRECT("'"&$C$1&"'!D12:D49")=$C12)*(INDIRECT("'"&$C$1&"'!E12:E49")=P$10),0),MATCH(1,(INDIRECT("'"&$C$1&"'!D12:T12")=P$9)*(INDIRECT("'"&$C$1&"'!D13:T13")=P$11),0))
But now I'm trying to modify so that it looks at all worksheets and will summarize the cell found in the index/match for all the worksheet where say cell C3 = myvalue,

And I can summarize all the cells say in cell H13 that match with something like this:
=SUMPRODUCT(SUMIF(INDIRECT("'"&$C$43:$C$92&"'!"&CELL("address",$C$3)),$C$3,INDIRECT("'"&$C$43:$C$92&"'!H14")))
But how do I then change it to add up not H14, but rather add up the cells from index/match?