First year's points aren't rigidly doled-out on a calendar year basis.
DVC usually goes back about 6-8 months from the resort opening. For resorts like Big Pine Key and
Disneyland Hotel which opened mid-year, the calendar year cutoff was pretty straightforward.
Riviera opened in December 2019. February and March Use Years did not receive their first points until 2020. April thru December did receive 2019 points. Many moons ago, the earliest buyers at Saratoga Springs were given the option of buying December 2003 points despite the resort not opening until May 2004. (This was a pretty big talking point back in the day because December SSR owners will actually get 51 years' of points, though they'll technically only have 2 months to use the last set before 1/31/2054. That came on the heels of BCV selling with the 2042 end date and only about 41 years of ownership.)
Given that resorts aren't available for all 12 months of most Use Years, it's a sensible way to try and balance. Some owners are technically getting points which start a few months before the resort even opens. The offset is others must wait until a few months after opening.