"So if a chip can calculate eight digits," explained Takehiro Izushi, "that's 7 segments [each number is built from 7 segments] times 8 digits for a total of 56 segments. And there's the decimal point and symbols like the minus sign. We made the Game & Watch: Ball game using a chip that could display 72 segments." And 28 of those went into the score/time display!
Elsewhere in the interview, the developers share early concept art for the devices (like the image above) and detail the process of making a new version of the Ball handheld for Club Nintendo.