At first I went and linked each artist’s track to it’s respected recording. But then I read the documentation on recordings and I think that’s wrong, because the tracks have been cut down for time, so I made them all new recordings.
Is this correct? It appears to be a DJ mix, or really a mixtape with very little (or no) remixing. But the tracks are cropped, so do these count as unique recordings? What if the mixtape didn’t have any cropping and they were all full length tracks ripped from other releases? Is it the cropping that makes it a unique recording?
A “few seconds” and they can get treated as the same Recording. Go too far and they should be separated. Each editor will give you a different reply as to what that crop level is.
Recordings of different durations can be merged, as long as there is no evidence to suggest that differences in mixing or editing have caused the change in lengths.
Variations in the length of silence at either end of tracks is not a reason to keep recordings separate, since no changes have been made to the audio itself. Similarly, different volume fades at either end of multiple tracks are not reasons to maintain separate recordings - they are considered mastering differences unless they cause the structure of the song to change. The same is true for variations in playback speed between recordings.
From the two tracks that I looked at, the lengths are different enough that I think that new recordings should be used:
I’d create separate recordings and add a disambiguation like “MURO DJ-mix” to each.
Just to mention it, MusicBrainz has different capitalization rules from Discogs. I’d follow Style / Language / English - MusicBrainz here since this appears to be a compilation of English-titled songs by (presumably) non-Japanese artists.
The guidance from Style / Language / Japanese - MusicBrainz to preserve the original capitalization applies to “names and titles originating in Japan”, which I don’t think is the case here… but even if it were, the tracklist on the back of the case uses all-caps Instead Of The Weird Discogs Style.
It looks like they are more than cropped, they are DJ-mixed, which means they are at least cross-faded ones into the others.
So there should be 40 new unique recordings, with a disambiguation comment saying part of “Diggin’ Brunswick” MERO DJ-mix, or something like that. Even if same length.