We typically perform some of our own testing for verification purposes of BAS, etc. However, I see no need for repetitive testing. If the CxA witnessed the functional performance tests and is satisfied that tests were properly carried out using properly calibrated equipment that should fulfill the project requirements.
This is where our industry as CxA is beginning to morph into something more meaningful than what has been done in the past. The emphasis now is on the Cx TEAM concept and we are expanding into the TBCx realm. It is no longer, a mechanical "TAB Only" process. Thanks, in part to LEED for opening the dialogue on enhanced type commissioning services. To me, the process remains the same, but the benefits to the owner are greatly enhanced.
My personal feelings, for what it's worth. The old TAB type of commissioning was of limited value, because without considering the envelope you are missing half of the picture. How can one successfully measure airflow, when one does not know it's origin?