How far in advance for award bookings? 1.5 years?

I have successfully created a booking for Jan of 2017 which is 18 months out from now. Anybody have any experience with creating award bookings that far out? Any issues with it?

I did a 5 night stay at the Hilton Bora Bora. I saw some reports of people trying this before the Hilton devaluation in 2013 but never saw any more commentary.