Excuse me to correct you, S.
PK turned TP on Jan. 12th (see activity) and has since played a bunch of rounds from amateur tees on STA plus some on CCC from Pro tees, in total about 43 rounds counting to the TP average, well saturated. This includes 11 scores below 70 from STA.
@TP, there ist an influence of a few Match wins against higher tiers (current average from strokeplay roundabout 70.7), but your description points towards the non-linear behaviour of your saturated average. It comprises your best 25 TP scores, and a new good score will kick out a higher score, dropping the average regardless.
I don't see any 73, you probably had the 74 at MER in mind. Before that, a possible highest score in the mix was a 39/78, and by replacing it, the average would have dropped by 4/25 = 0.16. You say it was more, but you have dropped your average about nine times this week with scores up to 77 - you may have overlooked it sometimes.
And, before you ask, a 67.00 average will safely make you a Master.