The Hidden Forest

I realize there's a Mod2 for backstab damage. This is not what I'm referring to. I'm looking at items like Immaculate Rubicite Breastplate that show a Backstab Dmg value as a stat. It doesn't display in the Webtools but if viewed in game it shows Backstab DMG: 25 with the default UI at least.

There's a handful of other items like this around Golden Leaf of Calamity for example that also have this value. Doesn't seem to do anything so I'm wondering if this is an display or other error or broken? My rogue's backstab damage seems to unchanged when wearing items of this type.

You are correct, BS Damage on anything other than your primary does not increase your damage. The key for rogue DPS is to get Backstab Damage as high as possible. I don't know if it's still true, however, if you donor out the max use to be 332.

I'm aware of how BS damage works.

I'm just curious why these items have this stat if it serves no function? Did it used to work, or was it always pointless? Is it just mod2 BS damage that got stuck in the wrong place, etc?

Just to verify this after double checking the code, your backstab damage will be based on the item you're wearing with the highest amount of backstab damage including the item's augs that have backstab damage. This will invariably be your primary weapon. In standard EqEmu and live (I assume) it checks primary weapon only.