darktable increases brightness in raw file with no way back

I own an old D2000/DCS 520. It is ISO less meaning ISO 200 or ISO 1600 will be the same when shutter speed and aperture are constant.

Original raw files end with .TIF but RawTherapee and darktable need .DCR to be able to edit them.

RawTherapee reads the files correctly.
Skärmbild från 2021-10-08 22-54-53

darktable doesn’t.

If I don’t remember it wrong darktable worked like RawTherapee last time I tried, 2018.
Download the raw files, change TIF to DCR and compare in RawTherapee and darktable. You can also try dcraw -E -4 -j -t 0 -s all 23HK3658.DCR to get a pgm file with all details in the highlights.

23HK3658.TIF (1.8 MB)
23HK3659.TIF (1.8 MB)

It seems that exiv2 isn’t able to get/show the ISO value and although both RT and DT use exiv2 this might explain why DT fails.

As a non-developer I can only assume that RT doesn’t (solely?) rely on exiv2 where DT seems to.

Even if exiv2 fails it doesn’t explain why I can’t get the details back. I haven’t yet tried to manipulate Exif.
Edit: tried to erase Exif with Exiftool. No support for .DCR files.