Comparing your GBK index to my tables reveals a few differences:
 
> 6 57 coq only FE10
> 6 58 coq only FE12
> 6 59 coq only FE11
> 6 60 coq only FE13
> 6 61 coq only FE14
> 6 62 coq only FE15
> 6 63 coq only FE16
> 6 76 coq only FE17
> 6 77 coq only FE18
> 6 83 coq only FE19
 
Vertical variants of punctuation marks in GBK/1 (GBK additions to GB2312, Row 6) missing from the index.  These were apparently missing from the original GBK standard.
 
> 8 28 coq only 1E3F
 
Another GBK/1 addition (ḿ).
 
> 203 96 annevk only 3000
 
An additional codepoint for ideographic space missing from my tables.  This looks a bit random, but (at least some) browsers do this, so I guess it is needed.  More information would be nice.
 
> 294 18 coq only 20087
> 294 19 coq only 20089
> 294 20 coq only 200CC
> 294 26 coq only 9FB4
> 294 34 coq only 9FB5
> 294 39 coq only 9FB6
> 294 40 coq only 9FB7
> 294 45 coq only 215D7
> 294 46 coq only 9FB8
> 294 55 coq only 2298F
> 294 63 coq only 9FB9
> 294 80 coq only 9FBA
> 294 81 coq only 241FE
> 294 96 coq only 9FBB
 
This is the entire Unihan G9 repertoire, 14 of the 101 non-Unicode 1.0 hanzi included at the end of GBK/4.
 
Apart from the ideographic space, the codepoints listed above all mapped to PUA or FFFD in browsers when I last checked (cf. <http://coq.no/character-tables/chinese-simplified/en> under GBK), but they render as expected in IE and should probably be added to the index.
 
Øistein