Some of them are on the Definitive Edition soundtrack (listed as Ori and the Blind Forest (Additional Soundtrack, free on Bandcamp). (Apologies if this is self-promotion, mods feel free to remove!)
e.g. #22 Title Screen (unused) - was actually our main menu music for about 1.5 years for internal builds. But really it's just a nice ambient tune that doesn't really have any lasting impact.
The main theme in its first fleshed out incarnation is # 21 (Launch Trailer - unused). It's a conceptual track that could have been used for a 60 second trailer. We then ended up using a version for this for our actual launch trailer, but a bit more epic in scope.
There's a bunch of material from track #21 onwards that were used for prototypes, or just never made it into the game.
At some point I'll do a Youtube video showing the original sketch and how it transitioned into what people know today.
It's partly luck, but also effort. I don't believe you can really 'fix' a piece of music if it fundamentally doesn't work. But in order to figure out whether it 'works' or not you have to actually start, develop, and finish the idea, at least to a reasonable level. A lot of them start out as piano sketches, but then they get fleshed out. Once the Ori theme that exists as you know it now got fleshed out, it was clearly the one that would end up winning the race. But until you have a body of work to choose from - for what to develop - you'll have a harder time getting to that point. Coming up with a melody - in my opinion - is partly luck, compositional knowledge/experience, but most of all, effort. However, this is just my approach, there are other composers who can turn out a jingle in a matter of minutes, and I envy them! That said, there is a difference between a jingle/motif and a melody (something that to me should be at least 4 measures long, and essentially combines/repeats related motifs into a cohesive whole). It's a massive topic which I won't derail this thread with!