https://www.sports-reference.com/blog/2019/03/2019-war-update/comment-page-1/#comment-259944
Baseball Reference has changed its calculation of pitcher's WAR back to 1960 to account for openers. They also changed their Park Factors to a rolling three-year average, which is a little strange given that the example they cite is that 2017 PFs are based on 2016 through 2018 numbers, which suggests that 2018 PF is based on 2017 through 2019. Finally, since they have a lot more data now available, they are able to incorporate SB, CS, E, PB into catcher's fielding from 1890 through 1952 and from 1935, on, they are able to include wild pitches. Prior to this update, catcher's fielding was based on errors and passed balls.
Baseball Reference has changed its calculation of pitcher's WAR back to 1960 to account for openers. They also changed their Park Factors to a rolling three-year average, which is a little strange given that the example they cite is that 2017 PFs are based on 2016 through 2018 numbers, which suggests that 2018 PF is based on 2017 through 2019. Finally, since they have a lot more data now available, they are able to incorporate SB, CS, E, PB into catcher's fielding from 1890 through 1952 and from 1935, on, they are able to include wild pitches. Prior to this update, catcher's fielding was based on errors and passed balls.