Yes, they did Slalom.
The story is a bit hazy for me because it's been a long time since I read it, but in Steve Kent's History of Video Games book Chris and Tim Stamper talk about how their relationship with Nintendo started. When they approached Nintendo to express an interest in developing for the NES, Nintendo, in all their racist glory, were very skeptical of these Brits and told them they could develop if they figured out the dev kit on their own. The Stampers plugged away at it and were not only successful, they found some programming tricks along the way that weren't well known. It gave them an edge over other developers in some areas, which is why their games look so slick.