Good question…

I’d argue this…

Let’s say you have 4 band members:

John, Paul, George, and Ringo

John drops out, is replaced by George^2.
Ringo drops out, replaced by Pete.
Paul drops out, replaced by Brian.
George drops out, replaced by Billy.

George^2, Pete, Brian, Billy.

You could argue they are still the same band as 3/4 of them each played with original members. Billy is the first to have never played with any of them.

Now… if George^2, Pete, and Brian get replaced, no, it’s not the same band.

I would add that also there should also be a connection between the art/music for them to be considered the same band

For example: Black Sabbath only changed their vocalist and they sound like two, quite, different bands. On the other hand, Iron Maiden also changed their vocalist and they sound like the same band with both Dickinson and Di'anno.

Or you look at Pink Floyd, Syd Barret, Roger Waters, Dave Gilmour, all vastly different sounds, yet all Floyd.

Are they really? Im not too familiar with pink floyd but they dont sound that different to me I even have trouble telling which "era" their songs are.

Syd Barret Era:

youtu.be/H6ci4pAYiUw

Roger Waters Era:

youtu.be/-0kcet4aPpQ

David Gilmour Era:

youtu.be/nVhNCTH8pDs