You would have to count mx11a as one of the promotional grades.

Almost all university graduates enter at mx13 if you are saying they are fresh out. So that's four promotions required to reach mx10 within 37 years.

Even if so, mx13 to 12 is auto one year timeline

So, 36yrs - (minus MX13 to MX12) - 3 promos. Say, 52yo promoted last time(even this is a "liberal" estimate), after 8 yrs promoted to MX11. Naturally take longer time to be promoted to 11a, and even longer interval to 10. In terms of increment sum and reaching salary bar early,it isn't a good thing to be promoted overly early. Which happened to many MX11a officers now. Possibility of no increment once reach bar, until promotion. Can be demotivating)
25-13
26-12
34-11
43 to 46-11a(9-12 yrs interval)
52 to 55-10(ie.7 to 10yrs official retirement age)

No NS. Grad in 2014. Promoted from MX13 to 12 with a B ... MI was 16% (over $600)! Is this normal?

If you mean normal as regular every year, no; if you mean it as promo from 13 to 12, yes.

True, but you are forgetting one thing-
If the promotion is early and you hit the salary ceiling early, it also means you get more money in the long run.

Yes and no, because every average cs of same calibre will go through this promo/increment timeline. All adds up for all cs under same scheme in the end, matter of earlier/later.

Nope it's no. There's a difference in total amount of pay at the end; the one who get promoted faster will get more.

I could only find the salary range for MX scheme in this forum. However, there was no bar mentioned. Can someone state salary range together with the bar?

What I know:
MX 12 - 2860-5874 (no bar)
MX 11 - 4735-7119 (no bar)
MX 11A- 6175-8555 (no bar)
MX 10 - 7001-11466(bar at 9975)