I have a main worksheet where I need to reference other worksheets in a formula, which won't be available until a date in the future. These additional sheets will all follow the same naming format, i.e. a three digit code, which I know already and have on my main sheet followed by the year, so for example the worksheet I need to reference could be called 6AE2013 or 6ET2013 and so on.

I want to set up the main sheet with all the formula in place, prior to the sheets (which are referenced in the formula) being received. I will comment all the formula out using a macro, and when they do arrive I can simply uncomment the formula and hey presto!

The problem I have is that rather than typing in each code into my formula, (there are several hundred different ones) because I know what the sheets will be called, I want to concatenate the sheet name within my formula, but I can't seem to get this to work. In Column C, I have a list of all my codes, I know my sheet name will be made from the code plus the year as shown above, but how do I concatenate this within my formula, the bits in red?

=IF('6AE2013'!$C$11="Construction",INDEX(INDEX('6AE2013'!$1:$1000,COLUMN(C1)+12,),ROW($C3)),"")
I tried 

=IF('CONCATENATE(C1,"2013")'!$C$11="Construction",INDEX(INDEX('CONCATENATE(C1,"2013")'!$1:$1000,COLUMN(C1)+12,),ROW($C3)),"")
and

=IF('C1&"2013"'!$C$11="Construction",INDEX(INDEX('C1&"2013"'!$1:$1000,COLUMN(C1)+12,),ROW($C3)),"")
but neither work. Is it possible to do this?

Many thanks