I think the sorting feature still needs work. I hate having to try to remember my most recent purchases when I'm online.
Why can I sort cars by date acquired when on single player offline, but when I'm online, that sorting option is gone?
The only thing I can think of is to add every recent car to my favorites and un-favorite them as they get older. That way I have a list of the cars I most recently purchased and still need to test and tune.