Why are you using DisplayCc ? in a Calendar appointment To = RequiredRecipients CC = Optional and BCC = Resources so for the information you need should always be in the strongly typed properties for https://learn.microsoft.com/en-us/exchange/client-developer/web-service-reference/optionalattendees
What your seeing with the DisplayCc is probably caused be the calendar Attendant making changes probably because of the privacy policy eg https://learn.microsoft.com/en-us/exchange/recipients-in-exchange-online/manage-resource-mailboxes.