The long-term orbits of comets can be difficult to calculate due to errors in the known trajectory that can accumulate from perturbations from the planets.
[2] Some lists retain the "C" prefix for comets of periods larger than about 30 years until their return is confirmed.
[3] While Jupiter-family comets are officially defined by 2 < TJupiter < 3, they can also be loosely defined as any comet with a period of less than 20 years, a relatively low inclination, and an orbit coinciding loosely with that of Jupiter.
These comets are often patchily observed, as orbital interactions with the planet often cause comets' orbits to become perturbed, causing them to not be found at the expected position in the sky and subsequently lost.
Additionally, their low cometary albedos and frequent proximity to the Sun compared to Oort Cloud comets cause them to much more quickly become depleted of volatiles, making them comparatively dimmer than comets with longer orbital periods.