Since 1920 (AP since 1940, other bodies prior to that). When paired with a team, the player must have been a 1st Team All-Pro in a season he appeared for that team. When paired with a non-team category, does not need to be in the same season.
So for 1940 and onwards only First Team All-Pro selections made by the Associated Press are counted. Prior to 1940, the selectors used to determine First Team All-Pro status are: