Importing Updates to Existing Products - Model Column Empty

Hi. I would like to bulk edit existing product descriptions. I have exported products using Settings > Import / Export XLS Tools.

The Model column is blank, meaning Model was never assigned to each product.

Upon reading Import Rules for Updating Existing Products, it states "If import system detects a product in your shop with same Model this will be edited."

My concern is if I now add Model for each product and do an import, will system create a new product or update existing? Does system attempt to detect other same fields (like SKU) before defaulting to create a new product? For example, if system detects same SKU, will this product be edited and Model field added?

Thank you in advance for any assistance with this matter. Much appreciated.

Which module are you using

Import / Export XLS Products Tool (V.5.6.0.0)