The tag usage data (including number of distinct values) is pulled from the Categorizable Tags aggregation generated for Perspectives. This aggregates all 13 months of available data, so it includes inactive assets as well.
Note: If CloudHealth permissions are not properly configured for an account or particular service, then CloudHealth will not have full visibility into all tags applied to any assets contained within that account. To avoid any issues, always ensure that your accounts are in a "Healthy" status within CloudHealth.