This is an interesting prototype in that the game has an internal checksum that is correct, and by and large, it looks complete. After investigating further, I discovered something very unique - this prototype is actually a transitional version between the released 1.0 and 1.1 versions of the game. The internal header has been changed to 1.1. Comparing the two revisions with the prototype, it is bitwise more similar to 1.0 version than the 1.1 version, though many of the changes in the binary persist between the prototype and the 1.1 version. It appears that all of the changes are within the program, and it makes it difficult to figure out exactly what has changed. In my quick run-through, I managed to trip the debugger at 0x1E1, which seems to be related to the loading of the fourth stage on the "normal" difficulty.
Anyways, the original ROM image I released had a copier header on it, I reuploaded the corrected image.
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