Anecdotally, over the summer (July/August 2018) I was using sensors with a use by date of April 2017 and a transmitter that I likely got at the same time as those sensors. Transmitter lasted close to its full life (crapped out about a week early) and I had minimal problems with the sensors.
I think this was definitely a “good luck” situation more so than a representation on how long they last though.