Some asteroid and comet discoveries of previous decades were "lost" because not enough observational data had been obtained at the time to determine a reliable enough orbit to know where to look for identification at future dates.
In May 1993, Marsden concluded that the trajectory of Comet Shoemaker-Levy 9 would put it onto a course to collide with Jupiter in July 1994, marking the first ever time that a cometary-planetary impact was successfully predicted.
[7] Marsden himself admitted the announcement was a strategy which needed "rethinking", and NASA asked astronomers not to sound a public alarm like that again but to communicate with each other.
Partly at his urging, the International Astronomical Union voted at a meeting in Prague in 2006 to designate Pluto and three asteroids “dwarf planets.”, which are objects that have not dynamically cleared their orbits of other debris (except, e.g., for collections of objects in stable dynamic libration at the "Lagrange-points", the libration points L4 and L5 of large, classical planets, as in the case of the Jovian "Trojan" asteroids).
[11] Brian credited his mother for inspiring his interest in astronomy when she showed him the partial solar eclipse of September 10, 1942; that the date and time could be projected far in advance very much impressed him.