I have had the new World of Hyatt credit card since it came out.
I had a 7 night Hyatt stay from December 27, 2018-January 3, 2019 (i.e., 5 nights in 2018 and 2 nights in 2019).
When the points and night credits posted from this stay, my WOH account showed that I have 7 night credits so far this year. I can't figure out if I was somehow given credit for all 7 nights of this stay in 2019 (which would be great) or if I got 2 nights for 2019 and the 5 nights for having the WOH card posted at the same time.
Another way of asking this question is does a stay that spans two different calendar years count toward the year that you check-out?