1) I use blue Loctite on the fixed cups of my Italian- and French-threaded bikes, because I did have problems with self-loosening fixed cups on my first Peugeot and my first Bianchi.
2) Make sure you can indeed obtain a satisfactory chainline.
3) Personally, I would demand a new frame. This is clearly a manufacturing defect.
4) Two years ago, on the Hetchins Heaven ride in Fallbrook, I was privileged to view a stunning collection two dozen Hetchins bicycles, one of which, from the mid-1970s, actually had the same defect as your frame.