Tracking exoplanets via orbital mechanics isn't easy. Plenty of variables could affect how a planet moves around its star, and determining which ones affect any given exoplanet requires a lot of data ...

Publications of the Astronomical Society of the Pacific Vol. 128, No. 962, 2016 April Orbital Period Investigations of Two W U... The orbital period changes of two W UMa-type binaries, AH Aur and V728 ...