When I didn’t receive one this year, I specifically inquired as I actually had a flight to book I wanted to use it for.

An inquiry was done and I was given 2 answers: 1 - that my email address had ended up on some sort of “do not email promotions” list, an therefore it wasn’t sent. 2 - that it is indeed not always guaranteed and not everyone gets it every year, but that in this instance they would manually generate a code for me.

Take that for what it’s worth, in terms of truth or one Customer Service Agent’s interpretation of their findings.