The missing dot is not just a thing that helps stabilize the colors in a picture, it's literally a missing dot. The first scanline is literally twitching left and right by one pixel every other frame. You probably can't see it on your TV without messing with the vertical hold.
It turns out which scanline counts as "first" depends on whether we're talking about SMPTE 170M (analog composite video) or Rec. 601 (digital composite video). Per the specifications, in 170M there are half lines but in Rec 601 there aren't.
Side rant, isn't that actually scanline 22? Scanline 21 is off-screen, its where closed captions used to come from...
But I'm also so used to it that I didn't realize a lot of examples were videos.
Really interesting investigation!