it is all random . there is no certain probability . you got 3 unique bolt quivers that can spawn on each roll ( Plague Gland/Larzuk's Bandolier/The Tranquilizer), so your chance must have been 1 in 3 rolls if something was certain , but it may aswell go for 10 or more rolls untll you get it , or you could be rolling it 3 times in a row .
it's called RNG (random number generator) for good reason . each roll is random . lucky for you there are just 3 options that can spawn . try crafting for a specific ring or amulet
