One is spelt Na
korn and the other is Na
khon
Although that is never a constant in Thailand because all names are a translation from Thai and the spelling of the English version is at the discretion of the person writing it.
A good example is Suvarnabhumi (Bangkok) airport. We would pronounce that as "Soo Varn a boo MEE" when it is really pronounced in Thai as "Soo wan a poom"..........go figure