It was probably so obvious no one replied to me, but in the event there is anyone wondering the same, my solution:
I sent an even invitation to the e-mail address of the calendar where I wanted to move it. Then I delete the event from the calendar where I don't want it WITHOUT notifying the cancellation. That allows me to change the event from one calendar to another. Since I use the "all calendars view" Now I know which cases are mine and which are not.