It's fairly easy to treat as well. All you need to do is get some cough medicine that contains codeine (sp), chemists own brand will do, and treat the dog with a childs dosage. Don't tell the chemist it's for the dog tho'.
Once treated, restrict the dogs exercise until clear and Bobs your uncle! Vets don't tell you this by the way. A local retired one told us.
It's the pulling on the lead and over exertion that makes it worse. You can tell if it's KC if you rub the throat just above the breast bone and the cough starts.
Hope that helps.
Ian