I've been using the Requirement to count the total of SCV. (As opposed to trained, killed, etc.) It seems that once the player has owned one SCV, however, the requirement becomes permanently met. If I kill the SCV that was owned, the ability to train another SCV remains permanently disabled.
Isn't there a way to make this work? By the logic I'm seeing, upgrades would permanently disappear even if you cancel them, and ghosts would be permanently buildable even if the ghost academy was destroyed.. Maybe looking at how cancel works will give me the answer.
EDIT: No way.. It can't be this easy.
EDIT: I figured it out by looking at the Ghost requirement for a tech lab and a ghost academy. It counts Completed for Ghost Academies!
Completed must mean the number of the unit in existence. Since one of the things that can be counted is Killed, Total must mean everything: Amount Completed and Killed. So Total is actually deceptive. If you want to count the number of units you own, count Completed.