Hi Thomas,
Here's what I have done in a similar situation. For your events create (if you don't already have) 2 date fields:Expected start and an Expected end.
Then make 2 formula date fields: Calendar Start and Calendar End.
Calendar Start = If(IsNull([Actual Start]),[Expected start],[Actual Start]),
Calendar End = If(IsNull([Actual End]),[Expected end],[Actual End]).
Base your calendar on these 2 fields.
If you don't have actual dates for an event, the calendar dates use the Expected dates. When you update your event with actual dates, the real event dates are displayed. You can color-code events if you make a status field (Tentative or Scheduled) based on what you have or haven't entered in the Actual Start field.
Hope this helps