This is True. ET Dept keeps the file of the car. If you are based in islamabad you can visit ET dept and check car file. For stolen car, You can visit 15 office and get verified from there.
Moreover, It is mandatory for the seller to visit ET Dept with buyer in order to get the car transferred on buyers name (unless of course you choose to bribe around 8-10k in case of seller absence). ET Islamabad only provides the transfer letter to the seller (on whose name car is registered). Even if transfer letter is issued, Seller is needed to be present in car transfer process.