” I don’t know how any non-godol can purport to know when a godol is incorrect.”
Well, for one thing many of us like to deal with these inconvenient things called facts and many of us have some specialized knowledge in certain narrow areas or fields. An expert can tell when anyone, even a godol is making a statement about something relating to their speciality without understanding certain facts. Thes e days the obvious examples are technology related but there are plenty of other examples
Just about the only field that I can think of gedolim being acknowledged by professionals in the field is medicine. And there only because of years of consulting with doctors to learn the ropes, not with asskanim