Hi.

Sorry, I didn't see this until just now. I already PM'd you on Twitch, but I'll say my piece here...

I proposed fixing this a few days ago, and Violet agreed to talk to GOG about this. My proposed fix is this:
Ultimately, since 1.3's only advantage over "Good" 1.2 is the presence of the Holiday Hare episode, I suggest a rollback to "Good" 1.2, then just fix the visible spring in Tubelectric 2 (it should be invisible) and the broken airboard ditch in Medivo 1 using J1E (I've volunteered to do this, and have already prepared a fixed Medivo), and replace Marbelara Secret with a copy from another version (say, 1.3). This would fix Orbitus 2, all the airboard ditches, and circumvent any issues from shipping "Good" 1.2 unmodified (since Marbelara Secret is unpassable if shipped untouched), restoring the original 6 episodes to how they were intended, while still keeping the 3 CD episodes.

Orbitus 2 should not be the nightmare it is, and that's not something that can be fixed by just making some adjustments to the 1.3 level file, as far as I'm aware -- my understanding is there was an engine change of some sort?... The only fan fixes out there make changes that alter the way the level was originally intended, whereas reverting to "Good" 1.2 would return it to how it was in 1.0/1.1, and fix most of the airboard ditches that are broken in 1.3, leaving only Medivo's ditch broken (fixable by just giving that ditch a sprite in J1E, like so), along with a screwy version of Tubelectric 2 (it has an extra section at the end, which is cool, but the spring at the beginning is visible instead of invisible, which suggests this is an earlier version of the level or something, so either we fix the spring and have the longer Tubelectric 2, or just swap in the version of Tube 2 from 1.3. Probably best go with the latter so it's just like it was in the original 6-episode floppy version), and a broken copy of Marbelara secret (which can be fixed by just swapping in the level file from another version, such as 1.3. Though I can't remember which Level file Marbelara secret is).

This would only require "Good 1.2", Marbelara from 1.3, some J1E modification of Medivo 1, and then one of those two solutions to Tubelectric 2 as well (likely best to just take the version from 1.3, to minimise the presence of fan-edited levels), and the result would be a version of Jazz lacking in any of the serious/game-breaking bugs present in the current GOG version, or indeed, any other CD-ROM version of Jazz. We would finally have an all-round good version of Jazz 1 that has all 9 CD-ROM episodes.

The other options have various issues; shipping any untouched version would have various issues this would lack, manually fixing 1.3 would require a lot of individual fixes that my method wouldn't require, meaning several levels (rather than just one) would be manually adjusted (which would require testing to make sure J1E didn't corrupt any sounds or anything like that), and most critically, Orbitus simply cannot be repaired in 1.3 without making serious level geometry changes in the broken section (such as the commonly-spread fix that completely removes all challenge from the section in question). Including multiple versions would likely be confusing, and I'm not sure GOG would go for it. Though if they're willing to ship multiple versions, it would be really great if they could ship 1.0 and/or 1.1 alongside a fixed 1.2; the Dreempipes thing would be appreciated by speedrunners, it seems, and if it's 1.0 rather than 1.1, then fans will love trying out the "APOGEE" cheat.

I do agree with adjusting the version number in the patched version. Perhaps it would make sense to call it version 1.4, or 1.2F, if possible. (1.4 since this is a version following the release of 1.3, or 1.2F because it's based off of the original 1.2 release)

The only thing this leaves is the potential issue of the fact that Holiday Hare '94 was included in 1.3, but isn't in 1.2, but this is easily fixed by simply adding Holiday Hare '94 to the GOG launcher autoexec batch thing. I've prepared a version of this to show how it could look, and as an additional fix, I've also added options to change the settings of the two Holiday Hares (currently, the GOG launcher only lets you change the settings of Jazz CD, not the included Holiday Hare '95, so that's another fix introduced by the changes I'm proposing).

The new launcher would look something like this:

(Though I now realise it says "What game do you want to run?", even though four of the seven options are not games. Still, easy fix)

As far as I'm aware, GOG haven't responded to Violet about this yet. In theory, as you note, the best case would be for GOG to be officially provided with all five versions, or just "Good" 1.2, and the fix can be constructed from officially-provided files, but if that isn't possible, I think we would all greatly appreciate you providing your version of "Good" 1.2.
IIRC Violet said to me that it might be easier if we can just give GOG an already-completely-ready "fixed version" they can use, so I was hoping to just dig around, grab a copy of "Good" 1.2, throw together the fixes in an afternoon, and send it to Violet to pass along... It's ended up being slightly more troublesome than that.

Sorry for the long post. There's a surprising amount of nuance to this.

EDIT: I just figured out a better way to fix the Medivo 1 airboard ditch, and have replaced the two links in this post with a link to that fix. Previously, the fix I used was to give the airboard ditch a sprite (I chose the invincibility star), since the way around the engine bug that makes the airboard ditch fail is for it to have a sprite. If it doesn't have a sprite, it doesn't trigger. I've now realised a few things about this: First, the sprite can instead be the shine/spark sprite, whose first frame is just two pixels in close proximity, so it's far less visible (bonus points for setting the animation speed value to -1 so it doesn't animate). Second, since the item's behaviour is "Face Jazz", if I set it to only have a left sprite, then the sprite will only be visible as you're walking through the event (that is, when you cease to be on the right, and start being on the left, the event switches to its left sprite, to face Jazz. Since I've given it no right sprite, this means it's invisible until you're half-way through walking through it). And finally, I realised that the small sprite I chose is hidden behind Jazz for the one frame it's visible before the game realises that Jazz is touching the sprite, and gets rid of it like an item, removing the airboard. So, the result of this new fix is that the airboard ditch appears to behave exactly as it did in 1.0 and 1.1, making this a seamless fix.