This was from a thread in C&V.
"And all mass produced items in which are brazed/soldered (same joining process, different temperatures) will be less than perfect. Soldering/brazing is highly dependent on the perfect fitting of parts. Brazing/soldering can not fill gaps (unlike welding) and so unless each part is milled or machined to perfect fit (nearly impossible in a factory setting - or any other for that matter), there will always be gaps in the joining process. So even if you inspect a brazed lug and it looks perfect doesn't mean that the unseen part of the joint is perfect, in most cases I seriously doubt that at any time there is a 100% bond in almost any mass produced bike frame from any time period.
Mind you I'm not a frame builder. But I am a welder by profession"