It is possible for new and returning drivers to sign up while the season is ongoing. They will do so on the lowest tier until it's full.
Switching cars
Drivers are given a grace period of 3 races to pick a car. The car you enter in race 4 is locked in for the rest of the season and cannot be changed.
DNFs & DNS:
All drivers must complete 75% of the race winner's laps in order to score points. Otherwise it will be considered DNF.
Standings:
Drivers are ranked in the standings based on how many points they've scored over the whole season. If two or more drivers are tied on points, the higher place in the standings will be given to the holder of most wins, and in case of tie, second places and so on.