You are under your license count. If you wanted to further reduce the number, you could retire computers that haven't checked in for 30 or 60 days based on the report we worked on earlier.
However, the best procedure would be to use asset management to track active assets (deployed in the organization) and retired assets (destroyed, recycled, returned to lessor, etc). You would then want your clients checking in to match the assets deployed. If you simply retire clients that haven't been checking in, you could accidentally begin ignoring active assets with broken agents.