Thanks.Pretty sure they do start with K. But I think they start the K count after they're done with the C** colonial tags. So, if the last colonial tag is C74, the first client state should be K75. You do see things like K01 later on in a save file, but I think they would only come into play if you cycle through K75-K99.
To be sure, enable "debug_mode" from the console, hover your mouse over a province, you'll see both the province number and the owner's tag.