If Wang's invention is completed while performing the task of the unit, although he will apply for a patent one year after leaving the factory, the patent right should belong to the unit.
The case mentioned that "the equipment for improving Japanese technology was produced and patented one year after leaving the factory". If Wang fails to improve the equipment before leaving the factory and can prove that his invention was completed after leaving the factory, the patent right shall belong to Wang.
If the invention was not granted Wang's patent right because of the technical publicity (the original paper mill also produced the same paper-making equipment after Wang left his post), and the original unit can prove that it has manufactured the same product before the application date, according to the second paragraph of Article 63 of the Patent Law, the original factory can continue production, which is not an infringement.
The above is just a personal opinion.