When we took our X in for service about a month ago, they just said it had arrived and gave it to us. Not sure if Tesla is still delivering the cover as standard equipment anymore. We also received the security cover that attaches on the back of the trunk hatch and covers the storage area above the trunk well. I've heard Tesla stopped including that cover as well, but i'm not 100% sure on that.
With the dark tint on the hatch, you really don't need a security cover back there because you can't see down into the trunk storage well.