Excuse me for not being an engineer, but wasnt the subject about Jack Stall, not Retreating Blade Stall??
We are used to thinking of aerodynamics as individual elements because it is usually more simple to understand them that way. The truth is that these individual elements interact and create behaviours that do not always manifest themselves as a single aerodynamic problem.
Retreating blade stall is not a simple problem of exceeding Vne. AOB, pitch/roll rate, main rotor RPM, atmospheric turbulence and other factors can cause RBS well below Vne. The classical indications of RBS are as Nick described (as ammended). The first indications are an increasing main rotor vibration at main rotor n/rev followed by increasing rates of longitudinal pitch-up acceleration and then finally the lateral roll tendencies of deep RBS. Hydraulic, SAS and some Autopilot systems can mask incipient retreating blade stall indications. Pilot control technique can aggravate or mitigate the onset of RBS.
Consider jack stall and retreating blade stall. Either one can be the cause of the other. Jack stall can cause the aircraft to pitch or roll in a way that causes retreating blade stall. The pitch up tendencies of RBS can cause jack stall.
Often RBS can be confused with main rotor tip mach, a more nasty problem in my opinion because there are few indications it is about to happen, and when it happens the rotor blade response becomes rather unpredictable.
Few books discuss RBS in a holistic way, most consider it as an individual problem and this might be what Heliport is alluding to - here the discussion usually covers all the salient points of interest.