Did it take much practice to be that wrong. The proof marks are not import marks, nor do they have anything to do with the United States in any way shape or form.
So what you are saying is Glock bothers to put adjustable sights on the slides of the parts they are importing so that the parts have enough points to be imported as a complete gun.....even though they are imported as parts? Is that seriously your argument?
In other words, you habe no idea what you are talking about.
The ATF regulates where parts are made, whether assembled here or not. Have a look at 922r. And if I'm wrong, call Glock in the morning smart guy. If you're right (which you're not), I'm sure we'll hear something by 9:15. If you're wrong, my bet is we won't hear from you at all. Get some spelling lessons too.