No, that doesn't follow. For most systems, a sensible algorithm would be "keep running the last known good definition, until we get the next known good definit

No, that doesn't follow. For most systems, a sensible algorithm would be "keep running the last known good definition, until we get the next known good definition" In other words: ignore bad updates but keep checking for valid ones. That doesn't mean you've permanently lost the ability to update. Of course, for some systems, different behavior might make more sense.