BOAC, it still unclear for everybody including 204 pilots and tech on both russian forums I read. There is mechanical lock on both levers and reverse deployment gears and tech people swear that link between levers and engine is mechanical. But it still seems that there may be conditions when if reverse levers are still locked by no wow signal, wrong manipulations with levers can send engine(s) to N thrust.
This is picture from Service Manual of ПС-90А engine
Pos. 13 is guide which move reverse flaps (as I understand it) and blocks max thrust deployment in intermediate position.