You might say, "When I went to vist them in 2002, they had a new car."
You would not say if the same persons had a new car currently, "They had a new car."
Now, how long is a "new car" new? That is more of a philosophical question? ;-)
Personally, I'd say about two years is how long I'd consider a car "new."
The phrase "brand new car" would limit that to less