Four Kepler groups with seasonal gaps retain 58–64% of three-transit phase coverage at 372.5 days for four 13-hour events with at least 50% coverage

We measure the phase coverage lost when a transit rule changes from three events to four. We fix five groups of ten Kepler stars from DR25 quarter flags and stellar cuts before outcome calculation. Four groups have seasonal gaps. The reference group has all 17 quarters. We use 720 public long-cadence files. A primary event lasts 13 hours and needs at least 50% coverage by finite PDC data with SAP_QUALITY = 0. Exact interval integration gives the phase coverage for a uniform event epoch. At 372.5 days, the four seasonal groups retain 57.85–64.15% of their three-event coverage under a four-event rule. A finite-baseline independent model with the same total eligible-center time gives 32.57–35.98%. Exact four-event coverage is 37.69–43.35%; the model gives 19.06–22.99%. At 365.25 days, retained coverage is 59.02–63.05% for the seasonal groups. The exact retained fraction exceeds the independent fraction in all four seasonal groups under four control rules at both periods. The package supplies exact three-event and four-event windows at 302 periods from 300 to 450 days, code, derived records, source hashes, figures, and independent checks. The general effect of recurring Kepler gaps is known. This study adds a fixed-sample comparison of three-event and four-event coverage. These values measure observation geometry. They do not measure signal recovery, planet occurrence, or a new planet detection.

Kepler · transit window · four transits · orbital phase · seasonal gaps · survey selection · public data · reproducible astronomy