I think it's a bit tougher than this. A good HR department--granted, many are not good--will always have a reason for any particular action.

In order to even tell, except in the largest companies, that there is a problem, let alone who was affected, you often need the company to do work up front in changing how they evaluate employees.

Otherwise, you will never even find that supposedly Patrick got promoted over Derek because Patrick had the best sales numbers even though Derek's team loved him more; but supposedly Robin got promoted over Allison because Robin's team loved her more even though Allison had better sales numbers. And so, of course, the actual reasons aren't making the difference.

So "follow the numbers" might work sometimes. Often not. And "act on them" is even harder. Better to get things structurally right from the start.