The major brands will have their own factories, building common modules and dropping them into the various shell sets/faceplate kits.
This means that every variant of the standard product you get from William DeMant subsidiaries gets made in the same place. It will have different writing on the outside for each distribution line but it’s the same thing. Different companies might write their EEPROM farther down the marketing ladder, but they can leave the factory as pretty identical product.
The interesting thing about the Sivdex combo; is though it’s a good territorial combination, the actual ethos of the companies is entirely different - especially WRT the environmental impact of product manufacture. Widex is renowned for being “windmade’ while the main Siemens factory was a huge building in Suzhou.