Before I dive into CD1 current progress I'd like to first talk a little bit about the lifetime of a single track - which should give you a better understanding about the pre-production tracklist "flux".
It all obviously starts with a "what if we had this/that version". Then I will begin looking for all possible sub-variations of that particular main theme version in my head - from time to time I would also refer to the actual episodes. Once I'm done extracting (still mentally) the bits that make those sub-variations different to each other, I try to glue them together and produce the very first rough mock-up version: the humming. Sometimes I'll use a stopwatch to get an early estimate of the track length. If it's too short - I restructure. If it's too long - well... that never really happened.
Once the structure and length make sense, I try to produce a MIDI mockup - usually using my trusty Yamaha CBX-K1XG which serves as a perfect scratch-pad with its ease of use and multitimbrality. This mockup obviously doesn't sound at all like the final studio version in terms of sounds; it focuses on accurate notes and track structure. At this point a lot of adjustments might happen - what works great in my head doesn't necessarily work in reality. When I'm more or less happy with what I'm hearing I will then put that mockup on my MP3 player and also submit it to Mark for evaluation (and yes, from time to time I even apply his suggestions!)
When the actual studio recording session is near (which, frankly, can happen years after) I'll start to listen to that mockup again to get "in the mood". The sessions always start from sound design - it can take hours or days before a particular sound is nailed - I sometimes even abandon work on one track and start working on another if I get stuck for too long. When the sound design is complete it's time to record my performance (i.e. the MIDI note data). I hardly ever recycle MIDI data from the mockup - the new sounds have different characteristics and require different treatment.
At this point it is still possible that I will find out that what worked in the mockup version doesn't really work in the final version with proper sounds and in extreme cases the track will get a decent overhaul with regards to its structure - in fact, no final version yet has been identical to the mockup (for instance, track 2 on the Airwolf Main Themes EP did not have the extra ending from 04:25 to 05:00). When that part of production is over with the audio recording and mastering is done. This can take up to several days per track, due to the nature of "replicas". I will explain this in another blog post.
P.S. The "years after" is no exaggeration. The first sketch of "Season 2/3 extended closing credits" was born on 12.06.2006, while I was on a train on my way to meet with Jean Michel Jarre. Audio recording started in November 2008 and was finalized in March 2009. There you go - over two years...