Meet the Pengarah of the JPJ branch.
Usually there's a list of "unclaimed" numbers

MB has it too
It's a way to give discount without angering those who bought new
It also enables the dealer to provide courtesy cars (low mileage, almost new pre-reg) or company cars to their directors, etc (usually about 1 year old)

But take not that most luxury brands has corporate discounts and do compare the value of the discount vs pre-reg

Actually, not all the numbers can be bought on mysikap and i'm not talking about single digit numbers. Popular numbers such as 8585 can't be bought on mysikap (unless things have changed)

Now the vehicle ownership cert doesn't show previous owner(s) anymore