When converting an additional contact to primary vs. swapping an additional contact with primary, the results are not the same.
These two functions work differently do to the differences between the CONTACT1 and CONTSUPP tables in the database. In the case of converting an additional contact to a contact, a new CONTACT1 record is created. However when swapping data GoldMine is trying where possible to exchange data in similar fields but there is no always a matching field.
In some case this does not work, by example when the additional contact is converted, information in the reference field is lost. This is because there is no Reference field to map too on a Primary Contact record. In such cases this data needs to be manually added to the record after the convert process has been completed.