GOUT is just a reference for which video frames to include. Lots of video/film releases are missing frames here and there, particularly at reel changes. In fact, the GOUT frames probably include more frames than anyone ever actually saw in theatres, but it is consistent (well, assuming you stick with NTSC or PAL…), and no other release is consistent with another, so “just pick a standard and stick with it” applies here.
So everyone syncs up their audio (and subtitles, natch) to the GOUT, and then as long as whoever releases the video makes it GOUT-synced, it all just works–video from one guy, audio from another, subtitles from a third. Makes the sort of informal cross-project collaboration we do around here easy. The problem is, if your video is missing GOUT frames, how do you fix that? Some will add black frames, some will add color-matched frames from a comparable alternate source. Some will just say to hell with it and not be GOUT synced. If your video has frames the GOUT doesn’t, that’s easy–just chop them out.
I have never been able to notice a one-frame sync difference (42 ms off). Probably because there are already ADR and SFX sync problems in the movies themselves, and a one-frame difference is less than that. A two-frame sync difference (83 ms off), however, is right on the edge of perception for me. It requires just the right sort of thing to be happening, but then I notice it. For other things, I don’t. Three frames is right out.
I wouldn’t sweat the 1 frame sync issue in ESB (but it’s also dead simple to fix, so why not?). ROTJ used to have a 2 frame sync problem that was bad enough I made my own audio files for it. IIRC, I never noticed it at all on SFX or the score, or even most dialogue–but every time Han spoke, it was obvious. I think it’s because Harrison Ford moves his mouth a lot (unlike Carrie Fisher), and he talks quickly (unlike Ian McDiarmid). It takes both factors for me to notice a two-frame offset. ESB also used to have a two-frame sync problem for a much smaller section of film, but Han didn’t speak during that part, so I never noticed.