I didn’t either. My youngest brother- then 16 or 17 traveled with me one year and he received a postcard at my house because my address was on the reservation. I called to use the pin and they said HE had to make the reservation and be present at check-in. This was impossible b/c he was not even old enough to rent a hotel room alone and not traveling with us!
I mentioned this to a CM recently and she said that as long as the person lives in your home, you can use the code. I also was told that if it comes to your address you can use it. It is attached to households now.
Maybe this is a case of different info from different CMs but 2 have told me I can use a pin code that comes to my house. Email may be a different story though.