It is clear the 1.3 and 2.0 created by source code level modifications. Another example the Super WP 2.5 from the Gmbh. I'm sure the German company got all sources from UK. This is our last hope: somebody from the Enterprise Computer Gmbh find us and have these.
Because you wrote the sad story: the IS is closed suddenly, and you can't save anything.
Many years (about 15) I emailed with David Levy and he is also told he not has anything about the Enterprise.

And the BASIC, EXOS, etc...
I started with the EXDOS because I wanted to work my IDE controller.
Unfortunately EXDOS Technical Documents are missing!
My IDE hw and the low level routines are ready at about 1996. But at this time I thought totally new DOS needed...
Many years later when I started the disassembly then found: expanding the EXDOS with new disk handlers is a very-very-very simple thing! Few days later the IDE interface worked with EXDOS
This is not the only reason! The other is: possible newer versions what we never see!

The UK companies collapse when happened? The UK EP magazine say summer 1986.
What did you worked after the 2.1 BASIC and EXOS finished until the collapse? (The 2.1 manual are dated as Jan. 1985. The EP128 with this version released at May 1985. I think some time needed for testing and produce ROM chips, probably these 4 months enought.)

Do you won it? (I'm not bid, before you wrote I thought about bidding.)

I guessed, EXDOS is then the EXOS+BASIC (mostly) finished.
The EXDOS developed with real machine? The first EXDOS card is looks like the real or it is a another wired prototype?

It sounds like a very interesting project! This is also in the IS?

About TVC DOS: what you known about UPM disk controller for the TVC?
The disk controller card is same with the VT-DOS. With additional UPM cartridge can run CP/M programs.
It is have own disk format, not a FAT standard. And under the BASIC just only used for LOAD/SAVE. For disk formating needed a system disk...

This come from the IS-DOS project? Or it is own project of the Videoton? If it is a Videoton project then they see the EXDOS is much better and ordered the VTDOS for the existing disk controller card?

It is clear the UPM is the older it is works on the TVC 32/64 models, the VT-DOS is only on the TVC 64+ (older computers can be modified by adding plus one IC to the paging circuit, then the VT-DOS will work).

The FAT standard is selected at the first step for the EXDOS? Did you see the future?
This selection made our disk life very easy! Especially now! When you download programs from the internet. Users of other systems (Spectrum, CPC, Commodore, Amiga, etc) have a hard work for creating disks for the real machines. But we just copy the files to standard disks and enjoy it on real EP!

And I can say: the EXDOS's FAT implementation probably the best on the world! I wrote many details about this to the Hungarian EXDOS topic.
Many times I saved damaged PC disks on the Enterprise just using simple COPY command... the EXDOS can really handle backup FAT copies!
After the collapse where you worked on the VTDOS? At home? Or the Videoton have own office in UK?
From the Videoton things you could have save anything?

And the MS-DOS 1.x not using standard boot sector (only type byte used), but the EXDOS also can read these disks. And also can read the non standard Apricot disks! I thought lot of in the disassembly at the boot sector analyzer part: what a crazy disks supported there??? Later found this is for early non standard MS-DOS what used by Apricot PCs.
You are used some Apricot machnies?

Absolutely yes!
Another great thing: at the Retry/Abort/Ignore case only the faulty sector rereaded. For example the MSDOS reread the whole sector group what used for the I/O operation. If more than one uncertain sectors in the group you probably never ending pressing the Retry in MSDOS because after the second error goto again to the first...
On Enterprise these disks usually copied with only few retries!

The IS-DOS manual also talking about MSX compatibility at the function calls. Probably some MSX programs can working on IS-DOS?
Yes this is worked well! Only problem when we made 11 sectors/track format. At this situation very minimal gaps between the sectors then needed a new rotation for every sectors, worked very-very slow... In my formater program I renumbered the sectors, every second is the next, with this method the track can be readed under two rotations, it is enought good. Later I found this idea called as interleave and commonly used at PCs with MFM hard disks.
Yes! And you got the damaged data, if it is in text or graphics file probably you can correct it.