That's odd. The code for the wolfram item syndrome is this:
[INORGANIC:WOLFRAM_COATING_ARMORY]
[USE_MATERIAL_TEMPLATE:STONE_VAPOR_TEMPLATE]
[STATE_NAME_ADJ:ALL_SOLID:Protection from Stun, given by the wolfram rune][STATE_NAME_ADJ:LIQUID:Protection from Stun, given by the wolfram rune][STATE_NAME_ADJ:GAS:Protection from Stun, given by the wolfram rune]
[MELTING_POINT:19000][BOILING_POINT:11905][SOLID_DENSITY:20][MATERIAL_VALUE:1]
[SYNDROME]
[SYN_NAME:rune]
[SYN_CONTACT] [SYN_INHALED]
[SYN_CLASS:DFHACK_ITEM_SYNDROME]
642: [SYN_AFFECTED_CREATURE:DWARF:ALL]
[SYN_AFFECTED_CLASS:DWARF_INTER]
[SYN_AFFECTED_CREATURE:DWARF:ALL]
[SYN_AFFECTED_CLASS:ALL_CREATURES]
[CE_ADD_TAG:PROB:100:NOSTUN:NO_SLEEP:START:0:END:498]
Which is fairly unique among the armory item syndromes in that it has an end defined, and a rather quick one, too. The only other one with an end is the gold rune, protection from dizziness. My immediate reading would be that it essentially doesn't work, because it ends shortly after it begins. A bug?
Also, since NO_SLEEP is in there as well, I guess it would be redundant to have both wolfram and chrome, if the wolfram were working.
The mithril one is less clear, though. The DF wiki says NOEXERT is supposed to prevent an entity becoming either over-exerted or tired from too many combat actions, and that's the tag the mithril coating grants. No oddity there with an END defined, either.
edit: The inclusion of an end may relate to this, from the wiki:
Creature can't be stunned. Creatures with this tag never wake up from sleep in Fortress Mode and stay drowsy. If this creature must eat and drink while playing, it WILL die.
Though since it has NO_SLEEP as well...I don't know.