The spec explicitly does not define the boundaries of all UB. Look at the note on the definition in 1.3.24 and the context of the surrounding definitions:

The spec explicitly does not define the boundaries of all UB. Look at the note on the definition in 1.3.24 and the context of the surrounding definitions: Undefined behavior may be expected when this International Standard omits any explicit definition of behavior... Rather than having specific causes, UB is simply the label given to "stuff outside the standard with no requirements whatsoever". Some of this stuff is important and much more of it isn't. A small subset of that infinite universe of UB is the set of enumerated undefined behaviors you're talking about, where the standard declines to specify any requirements in certain situations. These are what the annex is trying to organize.