Its in my Clymer. book # M447-2. It covers 82-91 125's and 250's, 500's 83-02. It says its a 1985.
They were just giving a simple letter designation that represented the model, which was the serial numbers in a range of say like yours Kx125DE000001 thru Kx125DE008400. D is just a quicker reference, even though everyone usually just uses the year it was made. Its just easier to be correct on the Year, when you go off of Serial numbers and their codes, so you don't wind up with the wrong parts.
