CxA to be an individual

Yes, the term CxA usually refers to an individual person.  Yes, for fundamental commissioning, the CxA for a project less than 20,000 square feet can be a member of the design team. The rules change for enhanced commissioning.

We used some definitions in my old company. The Cx Authority was the lead for the project, in charge of all aspects of the work and the one to ensure that proper QC was done and all aspects of our contract fulfilled. This was akin to the Project Manager on a design project. Then we also had a series of Cx Agents, who did testing, verifications, reviews, or whatever was assigned within their expertise and experience by the CxA authority. These were always named in our Cx documentation. I was often the Principal in Charge for the project. Agents who started doing more and more of the Cx would then naturally become Authorities as they were able and it became a growth path for staff.