Changing Document Names within Formulas

I have what I will call a "main" Excel spreadsheet that I want to pull information from other spreadsheets. I want each line on the main sheet to pull information from different spreadsheets that will be named numerically, i.e. 1001.exl, 1002.exl, etc. I have the first line on the main sheet pulling data from 1001.exl with specific cell references and that works great.

Now for the next line on the main sheet, I want to reference document 1002.exl but with the same cell references as before....just a different document. Of course if I edit and fill down, I get the 1001.exl document reference. How can I get the correct document references yet keep my cell references without having to do this manually.....it's a very long spreadsheet!