I have a 1982 Motobecane catalogue which references "inexternal" brazing, but only on the Mirage Sport which featured 2040 tubing. In the same catalogue, their top of the line models (Jubilee Sport; Grand Record; Le Champion; Prolight; Team Champion) were all "normally" brazed Vitus 888; Vitus 172; Vitus 979 and Columbus SL.
More "food" for thought......
Chuck Brooks
Malta, NY