A search for ἐστι finds many occurrences of ἐστιν. Also, a search for ἐστιν does not find the occurrences that appear in the results for ἐστι. As I look more closely, the search misses occurrences of ἐστιν that are adjacent to a Textual Note marker eg. ⸀ ⸃
In general, a search will not find any word adjacent to a Note marker defined in the SBL Apparatus.