There is no "luck buildup" as far as I know or have ever experienced.
Playing CT temporarily boosts a teams effectiveness. The following game the team will lose effectiveness. The level of boost to their effectiveness and the drop is based on the level of enthusiasm.
There is no cumulative effect of CTs. That would be silly. I am sure the games are correct. If anyone experiences anything in their own team that seems to backup this "luck" theory then come back with it.