I have never seen something that I knew was BT with a KB label. The only companies I've seen that I know for sure were Fratelli Toso and AVeM. I've also seen some generic Murano pieces, i.e., I don't know who made them. From what I've seen, KB usually imported lower shelf items, with the better of their pieces being the 1950-60s FT millefiori and AVeM tutti frutti pieces.
I sold a couple of these weights as BT back in my early days.

The last couple I sold I listed only as Murano, because I was no longer sure of the attribution. I'm leaning a lot more to FT now. Wish we could find one with a company label so we could know for sure.