SPA rules are based on law; once an agreement is reached it can not be changed because of opinion ... SPA is to prevent moving bar scheme
it can not be changed - FDA may rescind an SPA agreement ... because of opinion - the division director determines ... once an agreement is reached - after the trial has begun ...
The basis of your view - substantial scientific issue essential to rescind an SPA agreement - is false, you do not interpret the law correctly. It is B&W: "substantial scientific issue essential to determining the safety or efficacy of the product" ... means available science is not enough to determine the efficacy without any doubt.