NCC 95426610 USS MASON - Future Ship (30th century???)
One would hope that SF would have set a new registry system up long before they got to such ridiculously large numbers. Could you imagine how big the ships would have to be to fit them on? xD
If I remember correctly, it was Matt Jefferies that once explained the setup with the registries. The first two digits were the Starship class, the second two the number of that ship in the class.
Ie; The Constitution would have been the 17th Class of Starship in SF, so the first two digits would be 17. Being the prototype, it would be designated 00. This would give the registry of NCC-1700.
The Enterprise would be the first production model, gaining the last two digits 01, making it NCC-1701.
This can also be reflected by the Excelsior being NX/NCC-2000.
Of course, people then just started randomly slapping on numbers without much thought other than "That's my kids/partners/family members birthday" or some other event.