Knowing that all of your users will have Excel allows you to remove the DLL references from your project and convert your Excel references to "Objects" rather than hardcoded Excel objects. As long as you don't use a NEW function that isn't available in the earlier versions, this will work with all versions of Office.
For example, instead of this:
Dim _xlApp As Excel.Application
Dim _xlBook As Excel.Workbook
Dim _xlApp As Object 'Excel.Application
Dim _xlBook As Object 'Excel.Workbook
Everything works the same (except no intellisence) except for instantiation of the excel application:
_xlApp = CreateObject("Excel.Application") 'New Excel.Application
I have done it this way for 15 years without ever changing my code based on different versions.