When the Enterprise came back from its trip around the sun, there were two copies each of Captain Christopher and the Air Police Sergeant. I think the copies who knew too much were beamed into oblivion.
Lol - I never considered that... That may be Spock did pull Kirk and Scotty aside and say:
"We need to get rid of the anomalies on the ship that are Captain Christopher and the Sergeant. We can tell them we're going to beam them back to the locations we originally beamed them out of; but if Mr Scott would just cancel the remainder of the materialization procedure; that, logically, will take care of our problem, and both men will go on to do what they were supposed to do in history with no advance knowledge of the future..."

Works for me.
