The Alternate Parts Import is intended to allow for naming other suppliers’ parts that are equivalent to one of your parts. For example, if a part number in your catalog for an oil filter is equivalent to an oil filter supplied by another company, the table in the Alternate Parts section allows for the naming of the supplier, their part number and a description.
In this import, all four fields are required. The part number you want to link others to must exist in the global parts list (a new part will not be added as part of this import). The supplier, their part number and their description are necessary. The other supplier’s part numbers are not added to the global parts list for your catalog – this information would simply be additional information about a part that already exists in your data.