Index Match Erray - concatenating cells to create an array

Hello,

I was triyng to set an Index-Match formula which could automatically change reference sheet into a workbook based on an input (basically the sheet name). More specifically, I have 46 sheets (named from '1' to '46'). This is the formula that I've chosen:

=+INDEX("'"&LEFT($A275;FIND(",";$A275)-1)&"'!$O$71:$DL$71";;MATCH(I$274;'1'!$O$3:$DL$3;0))

Where:

A275 is the name of the sheet ('1' or '2' and so on until '46')

I274 is the input date

What the bolded part of the formula is trying to replicate is >> '1'!$O$71:$DL$71 <<

The formula results in a #REF

I was basically seeking for a formula that could change the reference sheet only for the array of the INDEX without referencing it manually for each of 46 sheets.

Could someone help me on this?

Thanks a lot