> version X+1 will remain backward compatible with X but may break compatibility with X-1

That is literally impossible; a breaking change from X-1 to X+1 must have been introduced in one of the intervals X-1 to X or X to X+1. It the latter, X+1 breaks compatibility, if the former, let X' = X-1 and X'+1 breaks compatibility.

Presumably you mean that X always includes warnings about breaking changes in X+1, which is a vast improvement on some projects, but knowing that a problem exists doesn't mean it doesn't exist.