For perspective...
When the Fiat 124 Sport Coupe registry was up and active, it took me about six years to register 483 cars in 37 countries. The production numbers on the Coupe are close to the X1/9, except that it went out of production in 1975. I would guess the X1/9, being more of a sports car instead of a coupe (think surviving BMW 2002 and Datsun 510), and being produced much later, has more surviving numbers. I also found that there are many owners who 1) Don't have internet service 2) Choose not to use the internet at all. You'll never find those people (and cars).
And yes, if you are wondering, the registry will be going online again.
Cheers,
Cesare