I was also a big fan of their Momo. Before that, there used to be a couple of Momo shops in Mahaboudha (near Bir Hospital) equally famous for its tase.
In my opinion, Everest Momo is popular because of its achar, so I don't think they will reveal the actual ingredients of this achar to anyone. If you are successful in a business because of a secret strategy, would you disclose that secret publicly?
Other factors that can affect the test are (but not limited to) brand of the ingredients you buy, its right proportion, timings while adding them etc.
Just my opinion.