Armor, Corrosive Damage, And Large-Area Injury
 

OK, Large-Area Injury (B400) covers situations where more then a single hit location is affected by an attack, chiefly area of effect attacks and while it handles the situation of determining the targets DR if it's not uniform it doesn't cover how to handle things if corrosive damage is dealt, in fact this problem extends to characters wearing armor even if the DR is uniform if the armor is piecemeal.

Take someone wearing armor light steal plate armor giving DR 3, and a player casts Rain of Acid over his location and rolls 5 damage, which is enough to remove 1 point from the armors DR, do I take one point away from every location, or just note it for future Large-Area Attacks? How do things change if the person was wearing light steal plate torso and helmet but medium leather (DR 2*) everywhere else?

Side note here that I'm assuming that the eyes with their DR 2 never count.

Re: Armor, Corrosive Damage, And Large-Area Injury
 

As the Raid of Acid hits to whole person, they'd lose DR1 off every location. If you were feeling kind and willing to deal with the bookkeeping, the soles of their boots might not be affected.

If they've plate on their body, and leather one their limbs, that changes nothing - after the acid bath the DR body is now DR4, and the DR2 limbs are now DR1.

As the Rain of Acid presumably comes down from above, unless their helmet is quite useless, it's fair to not consider their eyes.