Ah, yes, as I expected - as confusing as buggery!
The specific question relates the the KDX200, but more info/knowledge is always good. If I was to walk into my local shop and buy a new tyre for it, I'd just get a 100/100 (although I'd be happy with a 110/100 too).
However, I'm not prepared to spend $110+ on a tyre for it, so I'm looking at alternatives.
There's a guy advertising in Just Bikes offering cheap Chinese tyres, and I'm trying to work out which way to jump.
He's got 4.10 and 4.60 tyres in the olllllllddddd style Metzeler/Barum type pattern, and also 4.50s in the Dunlop K695 pattern.
I intend to buy a couple of the 4.10s for various non-race bikes (because the size is right and the pattern looks right on the older bikes, unlike a lot of more modern tyres). I bought a pair of the old style tyres from him ages ago, and the quality was OK - but I sold both of those tyres on bikes, so I can't refer back to them.