I'm bumping this thread up for you, to help get you some responses.
I do not know of any tarnish on gold and silver palladium hardware on H bags.
Some bracelets are made of silver and not silver palladium. So the former will tarnish because of oxidixation. But I was advised that I can take it back to Hermes anytime, and it will come back looking like brand new.
The palladium on one of my bags tarnishs and not the palladium on others. They are stored thes same way and place. Weird. I polish it and it just tarnishes again. I have a friend who has had the same experience. My gold hardware has never tarnished.
One of my gold charms is tarnishing, and it's only 3 years old. On some of the older bags, the fixtures are brass and so the hardware will tarnish, but i kinda like that. Vintage hardware looks great on a vintage bag IMO.
"This metal also does not react with oxygen at normal temperatures (and thus does not tarnish in air ). It lightly tarnishes in moist atmosphere containing sulfur."
All my bags have PH and none have showed signs of tarnishing (we live in a fairly normal climate--rainy at times but definitely not humid.) BUT I just received a guilloche double tour Kelly bracelet from Japan and I noticed that the turn knob shows sign of a little tarnishing on the interior of the circle.
interesting...I wonder if the general climate where you live affects the HW.? I have not had any tarnishing on any "H" so far. (silver tarnishes like MAD in my house...I am constantly polishing silver here! )