How to know if AF was on/off with playback?
 

Is there any indication or way to know while watching a tape if auto focus was on/off? Besindes watching the whole tape and looking for focus flucuations.

If there's a shot composed so the subject is off to one side and the focus is sharper for the background, then that would indicate the auto focus was on. Auto focus is center-weighted, so it will miss for most composition that is not also centered. That would be the only way to tell.