HEADERLESS_DATA_OFFSET is the value the offset takes in <lang>\etc\, not a property of the format. The leading stream is a whole number of 2048-byte XMA1 packets ending at the first RIFF, so its start is first_riff % XMA1_PACKET. Disc-wide that takes four values -- 1392, 1468, 1600, 1728 -- varying by language and subdirectory. Verified by decoding, not by arithmetic: on a random 140-bank sample with a non-empty leading region, the derived offset yields more audio in 85, identical in 54 (the eng\etc controls, where it must and does reproduce the old behaviour) and less in 1. Median gain among the improved is 70x -- eng\Voice\VOICE_TCAF_592 goes 1506 -> 97152 bytes, jpn 2910 -> 127178. This withdraws my own claim from earlier today that the Japanese banks were a different undecoded layout. They are the same format with a different offset; I had treated a constant derived from one subdirectory as a property of the format. The same error was hiding the identical defect in 1873 eng\Voice banks.