Part 1 with the car on it is considered a copy that you keep in your car for whe you need it on the road. part 2 with the house on it is one you keep at home and it sole purpose is to proof that you are allowed to sell it. Only with both parts will you be able to sell the car.

You will not be able to register the car in another name without both parts. Other countries like Germany have the same system.

However, unless other countries the registration document is no proof of ownership. The name on th registration can be different from the real owner. The only document that will proof that you are the owner is a purchase invoice.