In Splash, each contact is based on one unique identifier: their email address.

If a guest is imported into Splash with an email address that exists in the system but with a new First Name and/or Last Name, Splash will recognize this email and update any changed fields (as if you were correcting a misspelling).

This means that a new contact will not be created. Instead, the original contact will just be updated to reflect the changes you recently imported.