Thought so, cheers for clarifying. If I may correct you, both prototype music tracks of Lava Reef Zone aren't basically identical to final, and have some fairly significant differences. Someone on YouTube (Can't remember specifically who, sorry!) noted that Act 1 in the prototype apparently uses the same bass as Angel Island Zone's music tracks. The section right before Act 1's loop point also sounds a fair bit different, slightly more empty. Act 2 has a notably different synth sound, doesn't come across as high pitched compared to final, although that might just be instrumentation differences messing with my pitch perception. I'll agree that the prototype music tracks for Sandopolis Zone and Marble Garden Zone sound very close to final. Hydrocity Zone's prototype music tracks sound pretty similar to final as well, although I noticed Act 2 has some subtle differences in a lot of the foreground melody, sounds a hair quieter/less full.