Miles is correct as far as I can tell. But, imagine a car manufacturer having a long line of cars being assembled quickly proceeding toward the finish line and three people matching different engines for different vehicles going to different countries. And, after amassing hundreds of Honda 600’s from all over the world come to the conclusion that N600 and Z600 cars are a single run over 3+ years.
The chassis numbers are sequential, however because of the different rules for imports to different countries, engines are matched with these (sequential numbered vehicles) out of order. So the engine numbers give the true number of vehicles built for any country not the chassis numbers. And because all Honda 600’s coming to the USA have a date of manufacture (really the month) we have a good idea of what was made when and about how many. Then comes the capability for any dealership to install any motor at the dealership (new or used) and stamp a new tag with the correct chassis (VIN) with the new engine number. Yes, blank tags were available. But they were good about keeping the right transmission with the car. This didn’t happen often because the cars were literally throw-away cars.
Bill