A question for all you knowledgeable people out there: the micro-rotor watch modules of Calibres 11, 12, 14 and 15 were initially designed and manufactured by Buren. If this company ceased operations in 1972, then how Heuer and others were able to keep offering this type of automatic chronographs until the late 70's or early 80's? Did they produced the entire movement by themselves? Was it in turn manufactured by Hamilton or perhaps ETA (assuming that ETA was then already part of SSIH, now Swatch Group)?
Your comments will be appreciated.