The three stages would refer to a particular repunched mintmark made by a single die. The stage markers help identify repunched mintmarks as having come from that one die.
I do not see anything listed in variety vista for 1974S repunched mintmarks. I also don't see anything on your coin indicating that it is a repunched mintmark. You have to look for characteristics of the doubling, THEN look for particular markers - not the other way around. I don't see the doubling.