Whilst it is true the orbit of planets around a star do change, that can take thousands of years at least in the Sol System. But I guess that might not be the case for other star systems. But CA V and CA VI must have had a close orbit so that the explosion of one would cause a shift in orbit of the other. Of course Kahn might have thought it was a shift in orbit, but it could simply be that the explosion changed the axis of the planet and the resulting debris that fell on the planet kicked up a lot of dust into the atmosphere. And who knows perhaps the planet had high winds in the upper atmosphere that kept the dust cloud settling within a few years.
But even in our solar system with eight planets, numerous dwarf planets, an asteriod belt so we are talking about thousands of objects. We still managed to launch the Voyager II probe and it mananged to pass by not 1 not 2 not 3 but 4 planets because scientist where able to predict where each planet would be.