They probably have the three trains on a refurb schedule with one being out of use for a season, and another train the next, and so on. Great Adventure does this with Kingda Ka and the Runaway Mine Train. Sometimes towards the end of the season the fourth train for Kingda Ka and the third train for Runaway Mine Train appear on the transfers, partially or fully constructed. The next season one of the trains for each ride is taken off the track, giving the impression that one less train exists for each ride.