When you import from Excel and update existing records, that dataset will become the new source of truth for all columns you choose to import.
My suggestion is what while you may need to export all columns in order to see the complete information in excel, you should only import columns which which you plan to edit, for example those date columns.
You also may want to consider if there is a strong reason for doing these updates outside of Quick Base. Perhaps with some effort to develop some new Quick Base reports and using grid edit you can do the updates without the Excel export import.
