Is there a way to Purge/Clear client entry from the Network-Wide Client list?
What is the length of time that needs to pass before the Meraki dashboard considers them expired and removes them?
Can that process be preempted?
You could investigate the GPDR support.
You could also have a play with the group policy visibility option.
You could clone the network, move all the devices from the old to the new, and delete the old network, and it will start with no data. This would remove all the data immediately.
The Clients page displays client entries for the last 30 days as maximum.
If the target device is offline for longer than 30 days without generating traffic in the network, It would not be listed on the page anymore.
If you need to make the feature available to remove the individual client entry and the usage data from Clients page by manual, you may open a support case and ask to enable it from backend.
Hope this would help you out!
Looking at this on a wider view, there is no way to clear statistics on a network without creating a new network and moving the appliance. Sometimes you just want a fresh look. As a Enterprise Administrator the ability to do this would be helpful.