I dont know, but I happen to know for a fact that kotegaishi works just fine when someone has the mount on you.
Well yes, it does as does ikkio, nikkio, sankio and so on.
In fact it does works from either side of the mount.
The case of the two hand on the throat strangle is a good exemple. Especially since the natural tendancy is to put your boddy weigh at 90 degree of the arms (hence you are weakening your hip position and the control on the guy being mounted.
However, in my experience it is due to the guy in the mount rushing things or being inexperienced.
Any thing that is function of what Don mentioned will not give you the opportunity, basically if you are mounted; you are very likely buggered bar a cock up from the mounting side. It is not as bad in pure BJJ (i.e. were there is no pounding allowed) but it is still not a great position to be in.