How do I combine data in one spreadsheet from multiple spreadsheets?

I have multiple spreadsheets that I use and am trying to condense data into yet another "administrator" spreadsheet. Basically...trying to count the amount of accounts certain users have been assigned and have completed. I am using a SUMPRODUCT formula that links to each seperate spreadsheet and then populates the data in the new spreadsheet. Is this the better way? I feel as though having a "Sumproduct" formula in each individual cell of the administrator sheet is overkill. Thanks in advance. As you can probably tell, I am not advanced in Excel...but I do know my way around a bit.

Thank you.