Hmm, it doesn't really make sense. Every value i get ends up with about 10k ohm, which is the resistor i use.
For example 670 bit value from NTC = 10k ohm / 1000 = 10 as you said, and that's 25 degrees. But the temperature in reality should be 10 Celsius :S
Same goes with bit value 570, it equals 9986 ohms.. it equals about 25 degrees.