from my meager experience I’ll tell you that it doesn’t prevent it from coming loose,
If the grip panel and the bushing hole locations are to spec it will.
John Browning wasn't an idiot.
The grip will be a light press fit onto the frame, and provide positive support from below, and when thescrews are cinched down, will pull the lip against the side of the tube so that in the unlikely event that it does loosen, it won't walk out of the frame.
Some years ago an old gentleman brought a 1918 Black Army Colt to me for a teardown and inspection/cleaning. The gun had belonged to his father who was a veteran of The Great War, and he'd managed to get the pistol back home with him when he was discharged. When I took the left grip off, the plunger tube fell off on the table. According to him, it had been that way for years, but because the grip had held it in place, he didn't worry about it much. It wasn't repairable because the legs had rusted flush with the inside of the frame. I had a few NOS USGI surplus tubes on hand, so I replaced it. I doubt that it was period correct, but at least it was a GI-spec tube and it would have taken an expert to spot it. At the time, those old pistols didn't have the collector value that they have today anyway.
For this, the WW2 era synthetic stocks were better than the original wood stocks because they didn't shrink with age.
The tubes have to be properly staked, something that seems to have been lost in translation these days. You have to create a "well" in the holes for the legs to rivet into and pull the tube against the frame. You can do this one of two ways. Use a ball grinder on a Dremel to chamfer the holes lightly, or swage the chamfer with the tapered steel pins on the staking tool before staking the tube legs. I prefer the latter. It's easy to go too deep with the grinder and weaken the mount to the point of actually pulling through the frame or cracking it adjacent to the holes.
The other problem is that few grips are made to correct specs these days, but hard ones...plastic or wood...with a lip can be made to work by cutting a thin strip from shim stock and using it to provide support. If you're careful, it's not easily noticeable. In a pinch, you can even use cardboard, but it will need to be replaced periodically. Support from the bottom is most important. Support from the side is a typical Browning redundancy for a "just in case" situation.
the two legs/frame pins broke off of the tube pretty much at the joint with the tube. based on the appearance of face(s) of the two stubs left behind in the frame I'm just about certain that
