Recently, I learnt a few tricks and discovered a few characteristics of some videos. Still, I'm no expert and it will have to be a collective effort to figure out currently available content in various formats.

If enough interest, we can start a discussion here.

Let's see what's going on in this clip. I brought this youtube video into my VLC player. VLC's video info clearly states 25 fps. You said, audio is 4% slower than 25 fps field averaged DVD video.

And yet, both statements can be true. I'm not 100% sure but most likely my findings will be same as any one else's (Of course video tech who mastered this video, knows for sure). I tried to frame advance frame by frame. Somehow VLC video timer did not advance (other videos, it does). And, many frame advance you advance one frame but many are repeat frames, sometimes 3 at a time. So, if the played audio at normal speed and inserted frames and filled up 25 fps, you do get no 4% speed up as well as normal audio speed. Ingenious! I do not know if there is auto program for that or if they did it painstakingly, frame by frame.
Now, as far as lyp sinc is concerned, if a frame gets repeated 5-6 times in a one second period, you won't get the lyp sinc problem.

I'll look into other clips later on, one by one.

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BTW, filling up frames technique can also be used to replace/ add damaged frames with repeated frames. Only 14 frames are required per second to fool the eye. 24 frames film standard was used for cushion.