The Franklin is NX-326, yet was probably not created too long after the NX-01 and NX-02. Assuming the next four ships carried the names of NASA space shuttles as Enterprise and Columbia did--Challenger, Discovery, Atlantis, and Endeavour--one would also assume these ships would be NX-03 - NX-06. I find it hard to believe there were 300 more NX ships made until the Franklin was commissioned, so what are possible theories as to why the Franklin is NX-326?