(And, of course, that also means that NCC-1701 is only about 83% of the way towards being built.)
Naturally, not everything there has to be in the same class. Many different kinds of ships can have NCC numbers.
Well, I think that when the chart was made, it was probably just a bunch of numbers intended to represent all kinds of Starfleet vessels. I'm not really sure why Greg Jein, in coming up with numbers for all of the twelve Star Ships felt compelled to use all the numbers seen on that chart. I mean, it's not like ten of the twelve happened to be parked at Starbase 11. Other than the numbers that we did actually see or hear being used, I think the numbers should be taken with a grain of salt.