Jonathan Silverlight writes:

Can you imagine the feelings of astronomers if Charon hadn't been
discovered until 1990, and they realised they had missed a series of
eclipses which won't recur for over a century? :-)

Yes I can, because when the satellite was discovered in 1978, the
orbit was known to be nearly edge on, but it was not known whether
it was opening or closing, thus there was a 50 percent chance that
the eclipses had been missed.