Just to add to that, In the past when I have taken cars to be engineered, the engineer has said that sometimes the Registration Authority ( which ever state )
will stuff up and wont put the serial number on your rego sticker. To overcome this the engineers usually provide you with 2 copies of the certificate, one is for the Registration Authority and the other is your copy, and when you take your papers to the Registration Authority, have them stamp your copy to prove you have had it all passed and supplied them with the revelant information.