I only took one domestic flight in 2018 in Y, and I forgot to apply a RPU to the flight.
Received a CPU instead.
I don't even bother checking how many RPUs I have, as they all expire unused, every year.
Checked just now; I have 26 RPUs of which 8 will expire end of January.
Still, not interested in a complaint over this.
It's no skin off my back...
.....as long as I keep 100% success rate with my GPUs!