How about getting rid of this Cat ABCD rubbish altogether.
If people are getting through the RT/PC cyclic training program they should be automatically eligible for upgrade. Remove these subjective barriers and give people a go based on seniority.
If you've been an SO for 2-3 years or an FO for 10 years and you can't pass an upgrade course, whilst having satisfactorily completed every RT/PC along the way, the company needs to look at the upgrade training and checking programs - not blame the candidate's suitability.
Are there other airlines out there that use this system?