As per my experience, configmngr client is not aware of administrative UDA assignments,it is only aware, and creates a UDA entry in CCM_useraffinity, based on the automatic UDA assignment set in client settings.

As a consequence the requirement in DT for Primary DEvice/User only will be true based on usage at the client ( think if the users is able to set his primary device on soft center too).

It will be nice to create new entries at the client based on administrative assignment at the server, I think the best method should be a machine/user policy update where those policies include a check and create/remove Instances with updated info