Hard to argue with the manual, isn't it? Perhaps there's no reason to try...
I was having difficulty trying to account for the excellent accuracy of Kadet Kits that didn't need fitting, that just dropped in and which continued to work well when moved from one gun to another.
As we discussed this topic, you focused on barrel lug assembly fit to the frame while I focused how the front of the barrel assembly was controlled and how the slide stop restrained movement -- we were both focused on Kadet Kit to frame attachment but disagreed on the controlling mechanism.
After examining my Kadet Kit again, I think we're both wrong.
I think we've both overlooked the real source of the accuracy in these units: the barrel assembly and the sights are a locked, single unit; they can't move apart or be changed during the firing cycle . As long as you use the sights, the gun should hit where you point it, regardless of how the Kadet Kit unit attaches to the frame, or how tightly/snugly it is attached!
I think THAT design feature -- locked barrel/sight design -- explains why the Kit works so well, regardless of how tightly it is fit to the gun.