Proposal: adding unknown operational states

This is proposal related to the google doc issue 18.
Related text: "" .... and define an UNKNOWN state (is there probably already) ... "
(I think this was in theory agreed on, but the actual details need to be agreed on, before it can be added to the API)

This proposal adds such unknown operational states. These are, for example, used when  an AM can not know when a resource that was started will become ready.
I propose 4 different unknown states. Perhaps this is a bit much, and not all are needed, discussion is needed.

It was mentioned (I think by Marshall), that such an unknown operational state already exists. But I could not find any documentation or example on this. Does anyone have a reference?
Because if something already exists, this proposal probably needs to be changed to use the same state name.