You definitely want Media Agents and Access Nodes to match the CommServe.

Clients generally are not as important to keep updated, but you do want to upgrade them on some kind of regular basis so they do not fall too far behind on bug and security patches.

Thanks,
Scott
 

Make a conceivable plan that ensures even the clients get upgraded over a number of weeks in a controlled way, something you can manage should problems arise with anything upgraded. As Scott said, don’t leave them to fall way behind.

May I ask how you upgrade clients(You are referring to the servers we are backing up correct?)  What are access nodes?  

Does Commvault have instructions on how to do these updates?

Installing Commvault Software Updates on Demand
https://documentation.commvault.com/2023e/essential/installing_commvault_software_updates_on_demand.html

You will need to run a Download Software (or Copy Software) job to populate the Software Cache, and then you can push the update to the Clients.

Thanks,
Scott