It's not very user friendly to delete subs because of duplicate content, while the release naming is ignored.
How is a user holding
This.One.Movie.1999.1080p.BluRay.x264-THATGROUP
supposed to know that
Thismovie English.srt
subs for this release are wrongly timed (1000ms+ wrong), while
Thismovie [Sub] [Eng].srt
are proper but full of OCR typos, but if you did connect telepathically to OpenSubtitles.org admin's brain then you'll actually know the proper ones to download are
This.One.Movie.1999.720p.BRRip.DTS.H264-OTHERGROUP
or some other completely unguessable title.
It's not possible to know. So when a user uploads the best subs for This.One.Movie.1999.1080p.BluRay.x264-THATGROUP and they get deleted because "they are duplicates" you are forgetting one important aspect:
The user doesn't know this. Sure it's easy for you as admins to run a diff/whatever script to help detect it, but it does not help a user to find the proper subs at all. If you're unsure about this just make a poll, do you prefer to find your release name immediately, or spend 30 minutes hunting for proper subtitles.
A working solution would be as easy as just sym/hardlinking the release name to the now-detected dupe, costing zero disk space, but helping immensely everyone in possession of this exact release.
Comments etc are not a solution because they won't show in Kodi.
I'm not going to whine about "muh deleted uploads" because it's not about me but everyone finding their proper subs in the shortest possible time the easiest possible way.