flush out possible by phase

Hello the first phase (parking garage) of our project will be delivered to client for occupancy now, but the rest of the project will still be under construction for a while. we will apply IAQ Guidelines for occupied building under construction SMACNA. We might consider a flush out at the end of the project for the whole building, would it be still possible even if part of the building was occupied without flush out? or we have to flush out the completed phase (parking garage) now and seal it from the rest of the building that still under construction and then flush out the rest of the building when it is completed? please clarify Thank you!!