How about the programers/coders put in an IF Then Else statement for enlisting/unlisting cars so that it protects from accidents and keeps the garages clean. Something like
IF player's racing class is two classes or higher than a car in their garage
Then show unlist button
Else no unlist button shown
After finishing class E the average player only uses a car one class below as it is fully upgraded and easier to win points so by deleting car two classes below players can clean out older cars and only be left with class A and class B cars in the end.