Metter wrote
The same for me with my scooter- I have a copy of the original owner's NIK - I take that when I pay my annual tax. No problem at all.
As I understand it, the main issue is tax. The more vehicles one owns (tracked by the owner's NIK, or KK in places like Jakarta), the higher the amount for the subsequent vehicle's STNK. So if an original owner sells his car or bike and doesn't transfer title, and then buys another vehicle, and perhaps another, the tax rates on the subsequent vehicles keep increasing. So it's in the original owner's interest to insist on transfer of title. If they can't be arsed to do that then tough for them. Most locals get around this by registering additional vehicles in the names of family members (wife, parents, adult children etc), but this is more difficult in places like Jakarta, which use the KK to add up the number of vehicles a family owns.