none said:

The black bars are electronic, not part of the original capture which would have been 4x3 analog video.

How certain of this are you?

Oh, not certain at all. Such masking could, and is, applied when telecineing. These just look a bit too perfect, which makes me suspect they were generated electronically.

However they were created, the top and bottom black bars are probably not part of the original telecine. They are perfectly level, perfectly stable, and have a much sharper edge than anything else in the picture. In comparison, the left and right borders are original. The top masking is less severe, but we're clearly not seeing the actual bottom of the frame.

Again, I'd really have liked to see the raw telecine of this.

To sum up my observations about the Catnap version:

I believe this to be a telecine transfer, not a camcorded screening*.
The burn marks you spotted suggest from a release print (or duplicate).
That it has undergone some sort of post cleanup of the masking.
That the videotape source is very close to first generation.

*The runtime is 1:56:01 (from start of Fox fanfare to end of ratings card) matches the PAL speedup ratio. This seems conclusive evidence that this transfer is a telecine. If it was camcorded, even with a PAL camera, the running time would still be the theatrical 2+ hours.