there's a possiblity that the person in charge of the prize car project thought it was best to err on the side of inclusion, rather than exclusion, because once the deadline is passed, there is no way to go backto GT5 and complete them.
This sounds like something someone at work I know would do. State that you must complete the time trials, but then actually award the cars to anyone who is known to have logged on to GT5 during a certain period, just to make sure you don't piss anyone off. But then, that's not really PD's M.O, is it
But maybe they're learning