Don't see any way to move an email. Was thinking there was a way to save an email as a template like we use libraries, but there isn't.Is each attendee assigned to the correct invitation list?
When you create a new invitation list within an event, there is an option to "Use another list's emails". Select the invitation list that has the emails you would like copied to the new list. Be sure to set the Subject line and sender as needed as this is not copied in this process.
If you just need to copy a single email, begin to create the new email and choose the option to create from an existing email.
Another option is to create an email and then choose the action "copy content" and choose the email you want to copy. In this case be sure to update the Subject line as it is copied over from the source email.