Somewhat piggybacking on what someone else said: you should always have a fully executed copy of the entire contract itself, and in the worst case a copy that t

Somewhat piggybacking on what someone else said: you should always have a fully executed copy of the entire contract itself, and in the worst case a copy that the employer had signed (which is often enough). “Misplacing” an addendum can be a serious grounds for sanctions, but ideally you have the addendum with your copy and if possible there is additional evidence that there was an addendum, like perhaps contemporaneous notes or emails talking about the addendum.