When key issuance is fulfilled at individual locations, variations in processes exist. This can pose challenges with who gets access, what accesses they receive, and how you can keep track of them. If no uniform documented procedures or standards are followed, administrators are left challenged with how to fix the uncontrollable.
Start with developing standards and practices that are simple to follow using a centralized method of key control. When the key control information is uniformly collected and centralized, it becomes audit-able, allowing you to quickly mitigate concerns and regain control.
Here is a collection of content explaining how others have standardized their key control that can help you.