A fit with two harmonics to 31 early TOI-2202 b times has a 42-minute RMS error on 18 later transits

We test whether two harmonics improve a transit-time forecast for TOI-2202 b. We reuse 49 public transit times from a verified SCI data package. We fit 31 times through March 2023 and test 18 later times through September 2025. A weighted fit uses a linear clock and one or two harmonics. The fundamental period search covers 100 to 2000 days. Only the early fit error selects each forecast. The two-harmonic fit selects 725.26 days. Its later root mean square (RMS) error is 41.72 minutes, compared with 40.50 minutes for one harmonic. The largest later error is 75.16 minutes. The two-harmonic error remains 41.03 minutes with the original early published times and 42.64 minutes with a two-minute error floor. A separate fit to all 49 times has an RMS residual of 14.38 minutes and chi-square 5105.1 for 42 degrees of freedom. Thus, the tested second harmonic does not repair the forecast or give a fit at the quoted timing errors. A restricted two-planet timing and velocity search is also preserved. Its poor early fit and local search limits prevent rejection of the known two-planet system. This test is retrospective: the later data were visible when the study began. We provide code, input hashes, full period profiles, numerical checks, and all completed orbital trials. A related SCI study finds a similar forecast failure with a different timing sample and noise model. Our added result is this specific 49-time benchmark and its controls. The result is a forecast benchmark, not evidence for a new planet.

TOI-2202 · transit timing variations · TESS · forecast validation · harmonic models · radial velocities · reproducible research