099$t and 995$h are both indexed in ccode. I believe this is not good, as those two fields can contain different values. Is it possible to create a distinct index for 099$t ?
In standard configuration, 099$t is linked to "TYPEDOC" authorized values. So why not creating a typedoc index?
099$t isn't trying to be a ccode, it's trying to be a biblio-level itemtype without being an itemtype, as you discovered in bug 38336 *** This bug has been marked as a duplicate of bug 38336 ***