There are only the terms "restricted manoeuverability" and Not under Command
It is a kind of confusing the terms: "unmanoeuverable" or "dead in the water" and "limited manoeuverability", and "crippled" do not exist neither in the colregs nor otherwise. They exist however in plain English where peoples do not know or also the English is not good enough an so on (nothing to do now with not knowing better, it is maritime specific)
Restricted maneuverability means for example a dredger or a tug which tows or drills ships
at work,,but always when they are at work,, a dredger is not restricted when it not dredges
for example.
Not under command is a situation where a ship has a problem, usually of technical nature
this could include that for example it steers on manual rudder or the rudder can only
be operated to 15 degrees each side and not fully to the sides. Or the engine operates only
on ahead,,not astern anymore or only at 30% capacity. and so and so on.
Not under Command has therefore nothing to do with that the capt or officers are all drunk or if they don,t know who the owner is (actually not uncommon that at all, often crews know the operator, the crew agent but not the real owner)or if they don,t know otherwise what they are doing, which actually is also not seldom when one sees some situations