The main 200 AMP meter pedestal that connects to Edison has only one ground bar. Why would a subpanel need two?
I am talking about ground rods not ground bars. The requirement is 1 rod if the resistance is less than 25 ohms or 2 ground rods. It is easier and cheaper to do the 2 rods than prove to the inspector the resistance is less than 25 ohms.
Frankly based on you questions, you do not have appear to have the knowledge to do this job safely and meet code requirements.
Coastal South Carolina