the first off-roaders with fairings were Dakar-Bikes as these got bigger (first generation were XT 500s, XL 500s and similar modified bikes without such features). Introducing twin-cylinder-bikes with 750 and more cc suddenly speeds of 100 mph + were reached. You can't stand that flat-out a whole day without wind-protection. So for example HPN put a fork-mounted fairing on the big BMWs and there were also fairings put on bikes like Suzuki's DR 600. Afaik Honda had the first real purpose-built off-road-fairing on their NXR 750 - also to make the fast trip to Dakar a bit easier for the riders. Their Trans Alp must have been the first dual-sport-bike offered to the common customer with a feature like that at the end of 1986/beginning of 1987. Has been followed by Suzuki's DR Big in 1988 ...
Kind regards, Bambi
'Find me kindness, find me beauty, find me truth ...'
(Dreamtheater, Learning to live)