I wonder if the language on that letter - that refers to the ODD idea of carring that junk scrap piece of metal with you, bumping around in the car interior somewhere - really means that if the front one gets ripped off or stolen or defaced, that you can have a 'quick' way to put another valid one back. if you are ok with driving without one for the short duration it takes to go from where you parked (where the theft of front sticker happened) to where you stored your real metal front plate - that's your risk window, so to speak.
it just seems absurd to have to carry that, as a *requirement*. I see their intention, but I question the absolute need to have microsecond max latency between theft and replacement of a front. afertall, with a metal front, if that is stolen, its weeks or more before they send you another one.
IANAL, but that seems odd to me. I like the sticker - may get one - but totally laugh at carrying the metal front 'just in case'. absurd.
oh, and by forcing you to carry that actual letter - it also 'reminds' any helpful peace officer that you also 'need' that scrap metal junk with you, too. so, you could be cited for not having that, I guess, if they want to make trouble for you.
in some ways, it attracts attention and that's actually a Bad Thing(tm).