If they only did it on their under 550cc super-compact cars, they could be possibly telling the truth about it being limited to Japan only, Those cars are only sold in Japan because they don’t meet safety standards anywhere else in the world. However they keep selling them in Japan because they’re popular: inexpensive to buy, the yearly inspection (around $300/yr) is cheaper, they have good fuel economy, and most importantly you don’t need proof of a legal parking space to buy one (a requirement for buying a full-size car in Japan).
However I agree that it’s unlikely that if it worked so well on domestic cars that they wouldn’t do it on their foreign exports as well. Mitsubishi makes and exports lots trucks under their Fuso label, and they’re all diesel as well.
