I believe it counts for Q4. I am checking out on 2nd of January so will let you know. Anyway, my New Year's Eve stays have been surprisingly positive for me so far in terms of status / base / promo pts. Last year I scored Diamond having my base pts credited towards New Year. So they counted towards status of previous and new year.

Also previously I was staying in between of Quarter promos and the relevant date was check in date to consider whole stay as qualified under the promo that was valid when I checked in. But this can differ I guess.