Yes, the Retail Certificate of Sale is different from a Title to a car.
Documents used vary from state to state however a Certificate of Sale usually has to do with sales tax being paid on a vehicle, and is not the title of the car and thus cannot be used to sign the car over to anyone.
For example the New York Department of Motor Vehicles the proof of sales tax payment is made on the Retail Certificate of Sale document. It also includes an odometer disclosure statement on it.
In NYS a Certificate of Title is the official proof of ownership for a car, truck, motorcycle, motorboat, travel or utility trailer weighing 1,000 pounds or more, or manufactured home (mobile home). The title certificate is used to transfer ownership from one person to another. The title also lists any "lien holders" — those from whom the owner borrowed money to purchase the vehicle or manufactured home.
If you cannot find your Title to your vehicle, which normally you need to keep in a safe place along with other important papers such as a lock box, to sign over to the insurance company so that you can get your settlement for totaled vehicle you will need to contact your local Department of Motor Vehicles (DMV) to get a replacement or duplicate title.
When applying for the duplicate title if you cannot find your original you can get information from the DMV of how to properly sign it over to the insurance company giving you the settlement or the insurance company should be able to explain this procedure to you.