Well, AD and BC(E) are the usual notation in this case, but yes. This is distinct from -0 and +0 in computation, because as OP says these are intervals rather than points.

floating point arithmetic on computers does suffer the existence of a negative zero. But it’s generally considered an unfortunate consequence of IEEE754.

So in your idea there would be year +0 and year -0 before it, right?

Well, AD and BC(E) are the usual notation in this case, but yes. This is distinct from -0 and +0 in computation, because as OP says these are intervals rather than points.

floating point arithmetic on computers does suffer the existence of a negative zero. But it’s generally considered an unfortunate consequence of IEEE754.