How is (was) it possible that I have have a ZCM agent that is receiving bundles, shows Managed, and otherwise looking healthy, but is not found anywhere in ZCC?

In the workstation folder, I've done a wildcard search and it's nowhere to be found. I updated the agent with the latest 11.2.4 agent, and now it shows in ZCC. My concern is, how many more "managed" workstations might I have that aren't shown in ZCC?