Kenneth Chang

To make this make sense you really have to say that Cassini observed the spot with others until 1712, when he died; the others continued for a year afterwards.

Cassini and his successor at the observatory observed the spot until 1713. That's true. You're saying that the parenthetical somehow makes it not true.

If you use the word successor, instead of "others," now you're implying that Cassini's observation ceased before that date. If you say, however, "Cassini and others stood watching the paint dry for twelve hours (Cassini was indisposed and left after eight)," you have a problem.

There, "Cassini and others stood watching for twelve hours" is false, just as false as "I and 45 others have served as President of the United States." "Cassini and his successor watched the paint dry for twelve hours" would be fine because it indicates a switch midway.