belt of knives also work with a single weapon next to a tape, the weapon will buff the tape which will reflect the buff back to the weapon. so you don't need another weapon
Maybee I unterstand you wrong, but as you can see in the screenshot above on the right, after one hit, the dagger did not buff itself (no belt of knive) - or did I unterstand you wrong?
Atm its like this (floor 99, before Boss, cleaver just for fun I guess :p) 2nd Dagger was changed with Club before the Cleaver came in place (i know, there are not necessary, but they use belt of knive more effectivly (in my opinion) - at least atm :p