@yukari well, I'm English with a Westcountry dialect, and no one would think I missed the train if I said I "just about caught the train" (especially if you flip it into dialogue, eg: "did you catch the train?" "Just about!") One of the things about the English language is that it often contain implications that don't make logical sense, but add up to a larger picture. The "just about" to me, implies a narrow margin of success. And the opposite of "just about" is "nearly".