Already answered. https://ttlc.intuit.com/questions/3920953-i-adopted-a-girl-on-dec-8-2016-and-it-won-t-be-final-until...
Since the adoption is not final until 2017, you can claim 2015 expenses in 2016 (1 year late). In 2017 (if the adoption becomes final on schedule) you will claim your 2016 and 2017 expenses.
