In order for a custom league to be loaded into historic careers, it MUST have valid team keys. Here are the team keys you'll need to include with your teams (note, all the historic leagues have these values for 2025).

Dallas Cowboys DAL60
New York (N) Giants NY25
Philadelphia Eagles PHI33
Washington Commanders WAS32
Chicago Bears CHI19
Detroit Lions DET30
Green Bay Packers GB19
Minnesota Vikings MIN60
Atlanta Falcons ATL65
Carolina Panthers CAR93
New Orleans Saints NO66
Tampa Bay Buccaneers TAM74
Arizona Cardinals ARI98
Los Angeles (N) Rams LA36
San Francisco 49ers SF44
Seattle Seahawks SEA74


Buffalo Bills BUF59
Miami Dolphins MIA65
New England Patriots NE59
New York (A) Jets NY59
Baltimore Ravens BAL96
Cincinnati Bengals CIN67
Cleveland Browns CLE44
Pittsburgh Steelers PIT33
Houston Texans HOU99
Indianapolis Colts IND53
Jacksonville Jaguars JAC93
Tennessee Titans TEN59
Denver Broncos DEN59
Kansas City Chiefs KC59
Las Vegas Raiders LV60
Los Angeles (A) Chargers LA59