I might have run into this on a few systems, which started reporting first days of new year as 53rd week of 2021, instead of 2020.

Most systems behave as expected:

  $  date +%G.%V --date="03 Jan 2021 00:00:15"
  2020.53
  
  $  date +%G.%V --date="04 Jan 2021 00:00:15"
  2021.01