Good luck getting a straight answer on this!

From experience I 'd say its purely dependant on supplier. Dodgy ones will just call anything 'Stage whatever' just to flog them.
I bought a 2nd hand 'Stage 2' CVH head years ago only to find it very mildly ported with standard size valves.

I'd have thought valve sizes and porting would be the only main differences, obviously more work going in at each stage.
I dont think the cam has any bearing on things.