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Adobe Stock Contributor User Guide
Your nickname or display name only impacts the public facing portfolio page and the name displayed with your content. While you are in the contributor portaly, your Adobe ID name is listed. Changing your display name in the Adobe Stock contributor portal does not impact any information in your Adobe ID so while in the portal, your name shouldn't have changed unless you updated it at Adobe.com also.
Confirm your display name by clicking on one of your Adobe Stock files and seeing what is displayed as your name under the title of the file.