NFT Collection Maker Agency Upgrade adds the following 2 major features in your account:
1. Increase the per collection export ability to 20000 art pieces.
2. Ability to add up-to 5 Subaccounts.
So the best way to check if your NFT Collection Maker Agency upgrade is active or not is to check if you have access to Subaccount creation in your account.
So simply login to your NFT Collection Maker account. On the left hand side menu look for Subaccounts link below AGENCY. If you have a Subaccounts link, your Agency upgrade is already active.