Here’s an interesting article about how edition changes came about between Simplified and Diamond Jubilee. Most were teacher recommendations.
Another interesting study, this one by the government:
VARIATIONS FROM “STANDARD GREGG SHORTHAND” IN THE SIMPLIFIED EDITION WERE INVESTIGATED AFTER USE IN EMPLOYMENT TO DETERMINE INTERRELATIONSHIPS AND TO MODIFY AND REFINE THE “GREGG SHORTHAND SIMPLIFIED” PRINCIPLES AND PROCEDURES. SAMPLES OF SHORTHAND, WRITTEN BY WRITERS WHO HAD AT LEAST 2 YEARS OF INSTRUCTION IN “GREGG SHORTHAND SIMPLIFIED,” WERE PROCURED FROM NOTEBOOKS USED EVERYDAY ON THE JOB. EVIDENCE SUPPORTED THE HYPOTHESIS THAT, ALTHOUGH CERTAIN KEY ELEMENTS IN “GREGG SHORTHAND SIMPLIFED” ARE NOT FOLLOWED ACCURATELY, SHORTHAND WRITERS WRITE ESSENTIALLY TEXT SHORTHAND DURING EMPLOYMENT. IT WAS CONCLUDED THAT THE SIMPLIFED SHORTHAND, AS IT WAS TAUGHT, SERVED ITS PURPOSE