I Will Try Not To Make Your Eyes Roll in Back Of Your Head Or Make You Fall A Sleep As You Read This.
It Depends On What Tags You Have The Genre Saved In (Id3v1, id3v1.1, Id3v2, Other Tagging Systems).
CDDB DLL's Uses A Set Of Genres That Can Not Be Changed (Maybe The Program that Uses CDDB Can But The DLL's Have A Set Of Like 170 Fixed Genres) When Saved To the File Using The CDDb DLL's They Only Update The Id3v2 Fields. Some Programs Use There Own Id3 tagging DLL's And Not The Ones Built Into the CDDB Supplied Dll's
Also Not All programs Have Used The Standard ID3 tags (Like Music Match)
So It Is A but Hard To Answer Since We Do Not Know Where you Got the Files, Where They Were Ripped From, what was Used etc..
There May Be Some Tags That Were Saved With Old Tagging Systems (Again Music Match) They May Not Show Up Using MC Or Other Music Programs.
It May All Depend On What File Format Your Using, Not All Of Them Use ID3 Tagging.
But If You Rip The Files With MC And Save The Genre With MC Everything Should Be OK.