Correct, unknown hull # - so I put 7?? to denote 709, 710, 711 or 712.
Okay, I see now.
What was finally determined about country designation? Should all F16's sport the three letter country code?
All F16 compliant boats must show their 3 letter nation code and 3 digit sailnumber on both sides of their mainsail. The F16 class refers to the ISAF regulations for further details.
However these regulations are almost impossible to find for any normal sailor (don't we just love that ISAF organisation) so just go with what your builder is doing, teh F16 class will make contact with the builder if what he is doing is irregular.
By the way you will need to have a 3 digit number. so number 8 will have to be written down as 008. Or to be really precise. US boat #8 => USA 008
Be sure to become an F16 class member (still free of charge) and claim this number and secure your ballot voting rights. If you don't then you have no right to this sailnumber and anybody can take it away from you.
Wouter