Some track are never meant to come out and some things just don't quite make it. What is for sure however is that there comes a point where they are simply never going to be available. Not for love nor money.
As a genre drum & bass is maybe one of the worst when it comes to not releasing sought after music, be it absolutely huge anthems that get derailed by licensing issues or obscure masterpieces that appear once ever in that elusive recording of a DJ set. Somehow over 25 years or so we have amassed a library of music that should have made it to release but for whatever reason didn't make it.
I'm even guilty of it myself, I've signed tracks only to have issues later down the line, be it that the track just doesn't fit with what we end up doing at the time, or on one occasion we more or less completely fell out with the artist. I'm happy to say that the track in question did eventually come out on another label (which it really was better suited to) and we did manage to kiss and make up with the artist in question. Luckily, some unreleased tracks do find their way into the public domain through charitable people who like to share on Soundcloud. Here are just a few I've managed to find.
Pearson Sound - Windmills of Your Mind 
As Ramadanman, Pearson Sound was responsible for quite a few 170 BPM tracks that never came out, which is a great shame as his approach to the tempo is unlike any other. Rather than falling in-line with what everyone else was doing in 2008 he created "Windmills of Your Mind" which combines a whole host of bass related influences with some rigid drum work. I'm pretty sure the likes of Rinse FM's DJ Flight must have a whole folder of this stuff that never made it to release.
Instra:mental - Encke Gap 
The what? The Encke Gap, which is a 325-kilometre-wide gap within Saturn's rings apparently. Astronomy aside, this track is one of many Autonomic era tracks from Instra:mental that never made it out. In all fairness they probably made too much music to ever expect to release in any relative volume, but this is huge none the less. I remember hearing dBridge say he was lobbying to get some of it out, which I think resulted in "White Snares" finding it's way onto vinyl.
Instra:mental - Humanize The Machines 
Another prime piece of 170 BPM badness from Instra:mental. This one was showcased on the Autonomic podcast layer 02. Akin to a marching iron juggernaut, this one keeps thundering on relentlessly. I heard the term "gutterism" used to describe the music being made alongside dBridge and Consequence as The Binary Collective. I think it captures this sound quite well. Alas another track that will likely never see the light of day.
Blame - Planet Neptune VIP 
I love the original version of "Planet Neptune", I really think you can sense the influence of Deep Blue on it which maybe led to them collaborating on "Transitions" later on. I'm going to stick my neck out here and say that I think Dom (& Roland) might be involved in this VIP as it is much harder and busier than the original and he was prolific on Moving Shadow as an artist and remixer around this time. He remixed for Dead Calm, Deep Blue and Flytronix, while being one of the labels most prolific producers from 96 onwards, so he seems a likely candidate.
LTJ Bukem - Horizons (Paradox Remix) 
I don't think you can have a feature about unreleased drum & bass without mentioning Goodlooking Records. The track that is always sited is 1993's "Atmospherical Jubilancy", and it all starts from there really. Here we have Paradox on remix duties for what was also originally an early GLO classic "Horizons". Keeping the original vibe and splicing the beats paradox stays true to the original feel of the track. I really like this one and wish I had known about it sooner as it is new to me. Goodlooking fan boys must be seething.