The 2 options that are available when rating a sub are status quo and bad. Is there room for others qualificative? Such as maybe, just acceptable, etc… it would be a good tool when classifying the subs during the imaging night and before stacking.
At the imaging gathering phase, it’s usually either a good sub or a bad sub honestly. Like if there is some major airplane or some sort of mount shake or clearly out of focus.
Later you can blink through all the good ones and remove them again. Or use some sub frame evaluation to rate them further.
SGP includes an image grading program that will rank images based on number of stars, HFR. I often run it after an imaging session to weed out the really bad ones. Its under one of the menu selections.