Why No N-Number in FAA Database?

Hi all;

Checking into my first plane purchase, and have a question for you that I'm
not sure of.

I found a plane. I have not seen the registration cert (haven't looked for
it).

The N-number is *not* in the FAA aircraft registry database.

Why? I thought that registrations were good until changed - as in,
transferred to another owner, or if the a/c were totalled.

Thanks for any insight;
Carl