It is possible to make the Sum Excel formula reference another sheet, or multiple sheets, and add up a range of cells across those sheets.

A complex Excel 2007 workbook could require multiple sheets. By default, Microsoft provides three sheets on each workbook, but you can add as many as you need. Clicking the "Insert Worksheet ...

Microsoft Excel offers many ways for you to manipulate and organize data, including using multiple "sheets" or tabs within the same spreadsheet file.