The big5.ut (big5->unicode) table is based on CP950 plus Big5-2003. (i.e., mappings conflicted between Big5-2003 and CP950 still follow CP950 for compatibility ...
... Big5 Query Unicode Query Pinyin Query Symbol ... characters from character plane 7 and 86 characters from character plane 15. ... BIG5-2003 and various versions of ...
Unicode-at-on (Unicode補完計畫), formerly BIG5 extension, extends BIG-5 by altering code page tables, but uses the ChinaSea extensions starting with version 2.