2. The data of European majors are also incomplete. It is possible in recent years, and PCT is also possible, but it is still incomplete.
If you want to check a specific patent, you'd better go to the country where the patent is granted, so as to be accurate, not to mention the legal status must be the granting country.
4. General international search should at least check the United States, Japan, Britain, France, Germany, Russia, Switzerland, Germany, China, Europe and WIPO.