The column headings row (row 1 in the spreadsheet) is how the system matches up the data during import. So for the import to work correctly, the column headings must match the database information.
So, if you change a form field after receiving the import template, you must change the column heading to match. If you are at all unsure as to what the column heading should be:
Membership form
Click on the import link in the Membership summary section in Admin home
Choose the type of import, then download your customised import template. This will give you the correct column heading
Subscription form
Drop us an email and ask us to download your updated customised import template.