Multi-engine helicopter N2 simulation

Hello. I believe ENG ROTOR RPM:index is the correct variable to access the
N2 shaft RPM. (Not to be confused with my other question regarding N2: ) I find that this variable
reflects the N2 shaft, but that it is shared between multiple engines. In
reality the N2 shaft rpm can disconnect and fall away while the other engine
holds the rotor. Have I missed something which is joining the shafts? Right
now the simulation is capable of having either engine support the rotor, and
having load (torque) sharing… visible in Engines debug, but the N2 shaft
simulation seems to be missing behaviors.