Sophia here from Shopify. I would love to help you sort this out so that you don't have any duplicate vendor names.
Under Products > All products, there are two places you can view the vendors. The Product vendor drop-down menu in the filters section should not contain duplicates. The Vendor column on the far right lists the vendor for each individual product, so it is expected to see a vendor name more than once there if there are multiple products listed for that vendor.
If you see the same product name more than once in the Product vendor drop-down menu and the spelling is the same for each, double check to make sure there's no difference in the case. For example, if one is lowercase ("vendor name") and the other is uppercase ("VENDOR NAME"), that may be the cause for the duplicate. You can use the bulk editor to address and change any spelling or case differences.
Let me know if there's any more detail you can provide about the vendor names you're looking at. Is there somewhere else in the admin that you're seeing the vendor names listed, or was one of these areas where you noticed the duplicates?
Bulk editing products will only update the information that you change and save—any columns left untouched should not change. However, I advise getting in touch with our support team through the Shopify Help Center so we can take a closer look. I'm unable to access your account from this public space, but we're happy to help via live chat, email, or callback where we can authenticate the account and investigate to find out how these duplicate names appeared and work on a resolution with you.