Systems, methods, and computer storage media having computer-executable instructions embodied thereon that maintain a targetable user inventory for digital advertising. In embodiments, a request is made for user data associated with a user identification. If the user data or user identification is not available, a list of alternative user identifications is ranked according to various criteria based on identification signals. A match is selected from the list of alternative user identifications and user data associated with the alternative user identification is communicated in response to the request.