Some Continental tubes are made in Taiwan. They are made at a tire factory that produces MANY of the big, name brand tires that are on your dealers shelves. The Conti guys in Germany are VERY concerned about quality and, over a period of 2 years, with tons of Quality Control testing, they were finally won over buy this Taiwanese manufacturer. In short, these guys do a very good job.

Having said that, inherent in the industrial process are defective products. It happens to everyone in every industry. The difference between a good factory and a bad one is what percent of the production is defective. Even the best have defective products.

How is this relevant to you? Perhaps your dealer got some of a bad lot in their shipment. Maybe the next 3 tubes on the shelf were perfectly fine. It is possible. It does happen. Although I find it unlikely. What I suspect is that there is some other issue here.

You mentioned that you checked the valve hole in the rim. Did you also check you rimstrip? Some rimstrips (especially the yellow strappy kind that look like the straps used to bind newspapers or boxes) can have sharp edges. These usually come from the factory as original equipment (OE) on a bike. I have seen these cut valve stems before.