PB - if you get to Neg G you have a real problem - It should be noted that low G is where things start going wrong (IAS dependent)
Surely to say that every mast bumping incident results in blade separation is extreme.
There must be a magnitude of 'bump'.
On the subject of evidence of low G.
R22/R44/206 M/R blade just clipping tailcone could be evidence.
Damage of the droop stop/stops.
As sprocket said, on the 206, damage on the drag pin or striker plate missing is evidence of excessive mast vs airframe angle after mast contact.