FWIW & IMHO:
Could be several reasons. Of all the carfax's that i have done on turbobuicks over the last couple of years, I notice that a lot of records are quite sketchy prior to '90 or so.
Car may not have ever been registered.
Car might have been in the possession of a dealership for sale purposes, but never sold. It could have been sold but never registered, maybe. (just parked & stored).