Ephemeris are mankind's best efforts at predicting the behavior of comets. They take into consideration the direction and speed of a comet, when first sighted, and apply math that has proved true of previous comets. Most of the time this works. When it does not astronomers tell themselves a variable came into play, such as the gravitational pull of a nearby planet or that something internal within the comet caused it to behave in an abnormal manner. The ephemeris are assumed to be correct. They are not. Humans have backed into their formulas for explaining the motion of the planets, and gravity on the surface of their planet. They tried one theory on after another, until one seemed to work most of the time. Then they congratulate themselves on arriving at the ultimate answer, which will stay on the pedestal until it fails to answer some physical phenomena, new to their arena.
The human understanding of Orbital Physics is based on what they have observed. They backed into their understanding, their mathematical theories, based on what they had seen. Thus, when they plot the orbit of an object tracking in a familiar manner, they plot it reasonably well. This does not mean that the math is accurate or correct. It only means that their descriptions, up until now, have worked in the main. We are not saying that human equations fail to predict comet orbits. We say the base understanding of the full comet orbit is incomplete. We say the theories about where comets come from is incorrect. We say the explanation of why comets don't all go into the Sun is wrong. If the mailman comes by each morning about 10:00 o'clock, the child may make up any number of complicated theories about why and how the mailman's route is as it is. Then, when the mailman arrives the next day, on time, the child congratulates himself.
Ephemeris assume, first, that comets are attracted to the Sun, are aiming for it, but miss. What nonsense! Why do they miss? Did the Sun move out of the way? Where a planet the size of the 12th Planet is likewise aiming for the Sun but misses because of the repulsion force, smaller comets do not have the required mass to invoke a repulsion force in the Sun. Small comets miss because they by nature contain elements that are sensitive to the solar wind, and can no more come close to the Sun than can mankind walk forward into the full force of a hurricane. Is this not a form of repulsion force? It differs as the repulsion force is invoked in both parties involved in a potential collision, and the comet's sensitivity is a drama played out only in the comet. Essentially, elements within the solar wind push the comet away, keeping it at the distance it maintains from the Sun. Why does the solar wind not so push the Earth and other planets, or the debris in the Asteroid Belt? It does so push, but the planets by their size resist and the debris in the Asteroid Belt does not have the sensitivity that comets do. This is one reason, in fact, that they remain as debris and do not become comets.