maybe I'm missing something but this seems like much ado about (almost) nothing. If it really is a pot, it's probably either linear or audio taper. easy enough to find out with a couple of readings (don't turn it while taking a reading). If its an encoder, that should become apparent, too.
"readings vary from time to time" confuses me. does that mean that you can set the pot to a specific angle and then take two readings and get different results? I'd get another pot if that's the case. If turn it causes fluctuations in the resistance measurement, it may be a DMM sample problem or wiper noise.
"there are no limitation of degre" does that mean you can turn the pot more than 360 degrees? if so it is either a) broken, b) an encoder or c) a motor.
It's not clear what you want to do with this "pot". Maybe if you told us about the application we could help you.