If the SI is ever proven to be, as suggested on here, less than 100 % subjective, we would have to look at this again but, as it stands, I think the JC system worked
Freudian slip?
Every time I fly on an airliner these days, the safety brief mentions that turbulence can occur at any time, so whenever you are seated, you should keep your seatbelt loosely fastened.
With pilots also making occasional abrupt control inputs too!
Transportation Safety Board of Canada - Aviation Investigation Report A11F0012