Reply To: General Questions
This is tough one to answer for anyone not Jon, because there are so many ways to do this. Some things I can kind of go over, but keep in mind a: I'm probably using different equipment for mine, and b: Production and audio manipulation and production is my weakest field.
Generally, even with the basest of technology(I've got an old decrepit 4-track recorder around here somewhere that I've used), can be used to layer parts, so each track can be recorded separately. The two main ways to make sure things line up are having a click track, or hearing the other tracks as you're recording another one. After you do this, and I assume Jon uses digital recording over analog, because it really is amazing what you can do with audio manipulation in digital form. Even non-production software, like Finale(which is the program I spend 90% of my time in, when not rehearsing with performers or performing myself), has a lot of stuff that you can use to line things up. So I would imagine that once he records the tracks, he lines them all up in a program much akin to Garage Band. ProTools is the industry standard, so he probably uses that.
As for starting from scratch… whenever you change anything, you almost always have to re-record everything. Just recently I started doing a final pre-production revision of the score to my musical, and even then, I changed one chord progression from F C F C to Fadd2 Cadd2 Fadd2 Cadd2, but since I had triadic motion surrounding it, I had to change the measures leading up to it from D Em D Em to Dsus2 Em6 Dsus2 Em6, so that the general feel was preserved, and the measures after from Am C Dsus to Am7 Cadd2 Dsus, for the same reason. So a single change from chords built triadically to chords with a 2 added(which happens everywhere in the score, hence the change there) had such long-reaching consequences that the entire Chorus, minus the first two measures, was harmonically redone. If I had a recording, anything I had previously recorded would've had to have been thrown out.
Also, in Dance SJ Dance, the lyrics change between versions, so it would've been really hard to strip the track, and replace it.
Though if Jon had the inclination and time, any of the songs could be redone. Or if any fan had access to some nice technology or re-recorded a track based on what was done, the same could be done.