the correct sequence was Combat, Combat Star, Select and select Star.
On arrival there was pressure on for a crew to become qualified for QRA and this was usually achieved after a sqn cdr's check ride, and before the crew was Combat. There was no category for limited combat ready.
Then, in a 6 month period, jul-dec or jan-jun, the crew had to undertake a number of stats, different approaches, different navigation exercises and most crucially drop a number of bombs with a specific accuracy. These were 'classification' attacks on some targets. The crew had to be fully constituted (except for the copilot).
If the requirements were met the crew would then be awarded the next grade.
There was another difference later dropped.
A Combat crew was allocated 320 hrs per year whereas a Select Star crew ony got 280. Also some rangers were supposed to ge given to Combat crews, such as Norway for 2-3 days. Longer rangers such as Goose Bay or Akrotiri was for Combat Star and a Western Ranger to Offutt to Select Star. That was the theory.
But I was on Ops before I was Combat and my crew went on a Western Ranger before we were Select.