If I understand the situation correctly, I do not believe the out-of-the box Excel export/import will work for you the way you are wanting.
When the import is processed, if the SKU matches it updates the product. Otherwise, it creates a new product. Since you don't have a SKU - I would expect it to create new product entries.
See the manual here:
When an import file is processed, the software looks at each entry and compares it to existing products in the storefront. If the SKU of a product in the import file matches an existing product, that existing product is updated with the information from the new file. If there is no SKU match, then a new product is created with that information.