I subscribed to GT twice over the years & found their experiences & conclusions simply were not jibing with my own.
The one I recall as failing over a finish blemish was a Smith snub that had a tiny spot where the plating was starting to peel. Based on that, to the best of my recollection, the gun was deemed a "failure" & a lesser gun was chosen "best" of the two.
In another, the price was a determining factor, even though the slightly more expensive gun was a better fit for the task.
There have been numerous cases of comparing apples to cumquats that made no sense.
Their protocols & conclusions often show a lack of understanding of how a particular gun is used, with a corresponding faulty rating of "best" or a higher grade.
I know of one test sample obtained from the maker, no telling how many others have been.
Not all their revenue comes from the no-ads Gun Tests side, look at their sister on-line Gun Reports "publication" (link on their GT site). See any ads?
You also point out the problem inherent to a single-sample review.
That holds true whether with Gun Tests or any mainstream mag.
As I repeatedly repeat when this comes up, I'm not seeing hand-picked guns sent as samples. I've gotten clunkers & junkers, and so has GT.
Nature of the game.
I gave up on any further subscriptions with them.
Biting the hand that feeds?
I've cancelled several articles over the years because the guns weren't worth writing up. Only one maker has gotten snotty about it & pulled ads.
Your statement about using multiple info sources & your own judgement is right on.
Denis