Function left_out_note 

pub fn left_out_note(
    column: &ColumnDrift,
    dataset: &DatasetSchema,
    rows: usize,
    filtered: bool,
    sorted: bool,
) -> Note

Rows a filter or sort leaves out because their files do not hold the named column in its read type: the one note about the view. Phrased about the files (a footer fact), not as “the view is N rows shorter”, which an earlier filter may have made false; so it also appears where those rows were already gone.