You have a 20 race season, the manager who joined during the season break has the new start design of 24dp per race (480dp total) whereas the rest of you will only have 16dp per race for all races that were completed before the update. If the update happened after your final race the maximum dp you can have is 16dp x 20 races = 320dp.
For a fuller explanation see here...
https://igpmanager.com/forum-thread/61524