Frame drift on broadcast tape?

[90sTV]

Before ordering DVDs of a television series (which were made from transfers from network tapes of some sort), I had years ago bought some DVDs off the internet made by someone who captured them off TV broadcasts.

I recently noticed that the frames had drifted in some episodes of the "bootleg" DVD set (either to the left or right...usually left), cutting off part of the picture at one edge, compared to the release.

But here's the weird part - I looked at some uploaded clips from episodes people had recorded on VHS decades ago, and they were aligned in the exact same place as the "bootleg" set, which was captured years later.

So the frames apparently didn't drift on home-recorded VHS even after decades, yet somehow they didn't stay centered on the professional broadcast tapes? This seems backwards to me.

[JVRaines]

I don't understand. Which of the three sets — bootleg DVDs, home tapes, and official DVDs — are lined up wrong?

[90sTV]

The bootleg DVDs and VHS recordings have extra space at the margin (a light grayish-black section inside the black bar when viewed on a computer video player, pushing the frames slightly to one side or the other and cutting off some of the edge of the other side - usually the left side) where the official DVDs do not. And these bootleg DVDs/VHS recordings have them aligned in the same place.

[JVRaines]

So the horizontal timing was a little different from source to source when the master tapes were made. The home recordings, source of both your bootlegs and uploaded clips, faithfully recorded the offsets. But they would never have been visible on ordinary CRTs because of overscan. When the shows were professionally mastered for DVD release, they took time to shift and/or crop the shots to look consistent.

[90sTV]

So was the information for the parts that were cut off still on the broadcast tapes but just not captured with normal settings for the aspect ratio, hence it wasn't captured on the VHS conversions or bootleg DVDs, and hence they were able to retrieve it from those tapes and center the picture for the official DVDs, or was it missing from the broadcast tapes they used altogether, meaning the official DVDs would have needed to come from other tapes with different alignment?