You cannot put a strict definition on langauge because words have different meanings to different people at different times.
You can have a car built 50 years ago that was widely considered a pure sports car, but if you built the same car today it would no longer fit the definition because it may be too slow or handle too poorly.
Also, the definition is too loose to accurately categorize a car. For instance, most purists would say that a sports car can only have 2 seats. On the other hand, most people would also consider a McLaren F1 to be about as pure of a sports car as you're going to get... but it has 3 seats, it cannot be a sports car.
Definitions are too loose, and everyones' perceptions are different. The most you can hope for is for most people's perception to fit the definition as you see it.