One last tip that didn't make it into the manual:

When designing a fairly complex set of "chronological links" for 
campaign missions, at times the links can overlap. This can
sometimes look as if two missions are linked when they are not.
If you're unsure, here's a quick way to check. Just select one
of the two missions by clicking on it, and then click the "Break
Link" button. Any missions that are NOT dimmed are linked to the
currently selected mission. Then you can just click in a blank
area to cancel the link-breakage.
