The accessory drive system allowed only either fully engaged or fully disengaged which would make it more of a 'switch' affair
A clutch is defined as "Any of various devices for engaging and disengaging two working parts of a shaft or of a shaft and a driving mechanism."
Some models of the RR Merlin and Wright Cyclone piston engines, for example, have two speed superchargers with a "on, off" clutch mechanism for the change from high to low blower, or vice versa.
That confusion that exists as to what a clutch is can be seen in Kieth's post
I said that free power turbines do not need clutches
Free turbines do indeed need clutches, to cater for the engine failure case, if for nothing else. It is automatic in operation and disengages the engine drive from the rotor should the engine RPM ever fall below that of the rotor. The mechanism is often referred to as a "freewheel unit" and in all cases of which I am aware, is provided by a mechanism described as a "sprag clutch". A sprag clutch is defined as "A one-directional positive clutch design that connects two shafts when motion causes rotating elements located within races to wedge together. Rotation in the opposite direction disconnects the input and output shaft."
So all helicopters contain clutches, of one sort or another, and maybe to perform different functions. All certainly have a freewheel clutch mechanism, though I am given to education.
