In reference to the early round back alternators, the simplest way to tell exactly what your remanufactured alternator actually is made of is throw the stater on a scale. It's weight would be different.
Dang. Redfish, the scale is a great idea.
For the stators I had been trying look for visual clues (winding wire diameter, number of wires, color of coating)
At one time I went through a bunch of the FSM part numbers for stators and rotors to see which alternators they went in.
IIRC at least some of them had different rotors - at least by part number.
What I was doing last year was measuring field current draw and rotor resistance (slip ring to slip ring). It certainly revealed a big difference between original or at least correct rotors, and revised squareback and recent aftermarket rotors in general. Would not be surprised if it revealed some difference between various original/correct rotors for both roundback and squareback.
Both of those tests are pretty easy to do and don't require special equipment. Not sure why they scare a lot of guys off, but it shouldn't.