Stupid, but correct answer.

Can you improve on ironhands while wearing a shield. Not unarmed defense, ironhands.

Can you get a bonus (i.e. parry with) your hands using ironhands while wearing a shield.

I say no, Marcus says yes.

TWENTY INTERNETS RIDES ON THE OFFICIAL ANSWER. (hint: just say 'No to both, nt')

.IRONHANDS 'IRON HANDS'
Years of study and training in the art of barehand fighting causes bones
to strengthen and calluses to develop to such an extent that it becomes
possible to parry weapons with your hands.

In addition, this skill allows a significant advantage in landing punches
against foes who are less skilled at unarmed combat. Even assassins cannot
match a warrior who is dedicated to hand-to-hand combat. *** This advantage
requires that both hands be free, and it is much more effective if your foe
is also unarmed. ***

Helpfile probably needs to say 'These advantages'

Which means the helpfile is accurate as it is, and would be wrong with your suggested change.