If they can peg starting salaries for fresh graduate differently, i don't see how CEP has to be the same. In fact, the increase salary to the next range is bigger for you than a 2:1 NUS grad who started possible a few hundred dollars more.

If not, what do you determined your CEP - the 20-45 mins conversation you have before you start work? I think after all interviews, most people gets set on the default CEP based on a benchmark based on their background, and reviewed periodically.

Maybe the others in your department are better then that why the deserved to be promoted before you.