3) Japanese of that generation in martial arts have knowledge of sword. Yet to find one that doesn't. No justification. Common sense. Maybe most Americans in the relevant states have knowledge of guns.
As an American I can confidently say: no, knowledge of guns is not universal, even in parts of the country where gun ownership is common. And there are plenty of people who own guns but are completely incompetent in their use.
As for Japanese martial artists' knowledge of the sword, what is your metric? Willingness to be filmed waving a sword around? Or actual training to some degree of competence? As with guns, there can be a wide difference between real and perceived skill level.