Because of online multiplayer synchronization, Criterion patched all the DLC cars (Porsche 918 Spyder, Bugatti Veyron Super Sport, Lamborghini Aventador J, etc.) into the base game files years ago. The only thing locking you out of driving them is a simple 1 or 0 flag in your save profile.
If you own Need for Speed: Most Wanted on PC, do yourself a favor. Unlock the full garage. Take the Porsche 918 to the airport runway. Finally beat the 300 mph speed trap.
To this day, accessing the full roster of Fairhaven’s finest—namely the Ultimate Speed Pack , Terminal Velocity Pack , and Movie Legends Pack —requires a time machine back to the Xbox 360/PS3 storefronts or a hefty credit card for the "Complete Edition."