I was mostly successful, except for retrieving credits on sub-track basis (i.e., using HIDDEN_TRACKS sub-object).
I try to get them using something like
%<<TRACK_HIDDEN_TRACKS_CREDITS_ROLES>>%
or
%<<TRACK_HIDDEN_TRACKS_CREDITS_ARTISTS_NAME>>%
I immediately get an error.
However, this one works fine:
%<<TRACK_HIDDEN_TRACKS_CREDITS_ROLES_RAW>>%
I'm sorry, but I'm not really sure, I understand, what exactly data you want to retreive.
So it might be possible, my answer has nothing to do with your problem :-)
My formatting strings look like this (not sure atm, if those are default or my own...):
ARTIST:
$ifequal(%TRACK_TOTAL_HIDDEN_TRACKS%,0,$joinnames(%<ARTISTS_NAME>%,%<ARTISTS_JOIN>%),$join($unique($extend($array($joinnames(%<ARTISTS_NAME>%,%<ARTISTS_JOIN>%)),$joinnames(%<<TRACK_HIDDEN_TRACKS_ARTISTS_NAME>>%,%<<TRACK_HIDDEN_TRACKS_ARTISTS_JOIN>>%))),' / '))
TITLE:
$ifequal(%TRACK_TOTAL_HIDDEN_TRACKS%,0,%TRACK_TITLE%,$join($extend($array(%TRACK_TITLE%),%<TRACK_HIDDEN_TRACKS_TITLE>%),' / '))
Other than that, I have not used any *HIDDEN_TRACKS* references in my formatting strings and I have not missed any important information in my tags. Until now :-)
Maybe you point out, what information exactly you want to get, i.e. name/link a release and show us what you want.