General

60% boss damage? Night raven claw

I'm about to buy a night raven claw from a friend, but i thought boss damage didn't stack? Can anyone confirm that?
And can i have a price check please?

Stats;
3 dex
3luk
61 att
0 slot, 2 hammers used
1 time enhanced

3 lines pot;
30% boss dmg
30% boss dmg
6% int

thanks