I don't know about the video sources, but I can tell you the audio tracks in the 1989 SWE versions are not the same as the JSC. The analog-to-digital conversion used for the PCM tracks on the earlier laserdiscs is of lesser quality, with insufficient anti-alias filtering and no dither. Low levels of digital distortion are present, and the EQ pushes the high frequencies too much, resulting in a somewhat thin sound.

All these characteristics are typical of CD releases from the 80's, since they would have been made using the same type of equipment.

By contrast, the SWE features a more robust EQ and does not seem to have any digital distortion. It is also somewhat more dynamic, despite being the same mix. The amount of tape hiss is higher, indicating it may have come from a different analog source; there are also occasional dropouts, and at least one reel seems to have been transferred at the wrong level compared to the others, but overall it definitely sounds better.

These observations were made in the course of GOUT-synching the 35mm mix of ESB for Harmy's DeEd v2.0. I chose the SWE for the reasons listed above, and did all I could to repair its faults and create a more consistent track throughout. I haven't heard every laserdisc version out there, but the SWE sounds the best of those transferred by schorman13 for his archive. So far I've only closely scrutinized ESB and haven't compared the tracks for the other two films, but it seems reasonable to expect them to show similar characteristics.

I'm not sure what other conclusions can be drawn from this information, but hopefully it contributes somewhat to the discussion of differences between versions.