Surely the Tristar predated GPS by some years.
apologies. Quite right. INS ground speed. Just as accurate though. And on 737-200 we had Doppler ground speed - and 707. Pretty accurate too!
GPS ground speed will get you out of trouble in all these cases of chaotic airspeeds/stickshakers etc. Couple it with pitch and power and you actually cannot stall or over speed. Maintain ground speed at time of failure.