Currently, the release date/year for a release group is defined by the first release overall, including promotional and bootleg releases. However, oftentimes, releases leak early or advance promo releases are made for pressing plants, and the release date is not actually set as when it officially came out to the general public. It's not as big of a deal when the leak is the same year, but in many cases, it changes the year of the release group on the artist's page.

e.g. Miss Anthropocene (2020) has a bootleg release from 2019, so on the artist page for Grimes, it says it's a 2019 album.

If we made it so official release groups get their date only from the official and withdrawn releases, the release group would have the correct year of 2020.

 

Perhaps, we could include bootleg & promo release dates when you select "view all releases" on the artist page. Not when showing only official rgs though.