Hi, Bryan McGrail
Good day!
Thank you for posting to Microsoft Community. We are happy to assist you.
According to your description, the issue of your concern relates to the Outlook Delegate Access.
First of all, it is feasible to create an event/meeting for the past days through my test as below picture:

Please be kindly to understand that in Outlook, there are three delegate permission levels as below:

If you stop the user to do the above, please be kindly to ask your Boss to change permissions for a delegate as following steps:
- Click the File tab.
- Click Account Settings, and then click Delegate Access.
- Click the name of the delegate for whom you want to change permissions, and then click Permissions.
**Note:**If you want to remove all Delegate Access permissions, don’t click Permissions but instead click Remove and skip the rest of these steps.
- Change the permissions for any Outlook folder that the delegate has access to.
- To send a message to notify the delegate of the changed permissions, select the Automatically send a message to delegate summarizing these permissions check box.
We're glad to assist you and please feel free to contact us if you need further assistance.
Sincerely,
Alex | Microsoft Community Moderator.