I have more than half a dozen GPSDO in my lab. If I average each for 24 hours, they are accurate and precise, but instantaneous reading is all over the place. With two, you can potentially average. With three or more, you can do N-cornered hat. But verifying each method is actually working in home lab is entirely different matter. You'll need a reference guaranteed to be accurate and precise than DUT. Still, I think about putting dozen of them and do some kind of scheme, but I doubt there is any practical value in such attempt.