Portion of formula in another cell

I am attempting to use a formula which has a part of the formula contained in another cell. The desired formula (which does not work would look like this:

'=SUMPRODUCT(--(CONCATENATE("[ProjectNumber",$A$3,".xlsm]MasterCityData")!A1:A1)*1)

where "$A$3" is the name of the worksheet [using the '=MID(CELL("filename",$C$1),FIND("]",CELL("filename",$C$1))+1,256) technique].

I believe that I have attached two files which explain the problem more thoroughly.

Thanks, Dell.