Im no expert, but was involved a little in the early days, with some of the guys from cumbria, wales and norfolk. But lets not get carried away with the word rough coated. Id say broken or even a course coat. Alot of the dogs had like a thick undercoat.
When Brian first started he tried a variety of dogs, including the immal terriers, jacks and bull breeds with developments over the years and different clubs, all sorts of good and bad traits were taken out or developed further, to irradicate putty nose and Tri colour and a number of things, But Im quite sure now that it is as much a true bree