The GC-ADPCM format relies on some numeric coefficients. I posted them in a previous post, but it's possible that every sample has different coefficients. I also don't know about the "previous" values, whether they're the same or not for all tracks.
I think it should be possible to decode it (not perfectly) as a single long file.
I think it should be possible to decode it (not perfectly) as a single long file.