The reason you cannot use the same number field multiple times in one form is that these fields have a 1:1 relationship and can only ever be used once per form so that the numbers do not overwrite each other when the form is brought into GIFTS Online.

If you wish to bring more numbers in, we would advise constructing custom fields to account for these - this can be done if you subscribe to the Blueprint module or through our Services Desk as a billable service.