The problem is not so much how often it has been required but that it is used as a mitigation in the hierarchy of risk for the airframe.
If it has been demonstrated that the device cannot be used to perform the risk control as stated then EITHER the risk has to be entirely reassessed, another control put in or the trim wheel re-engineered.
If the risk assessment for the NG (and MAX) is unchanged from previous versions for the elements of flight for which the manual trim wheel is a control then the assessments for these will also have to be redone or another control put in.
Either way a big big task for Boeing and regulatory authorities.
Last edited by Maninthebar; 18th Jul 2019 at 10:30.