def validate_distance_data(data):
    """Validate distance data is both present and non-contradicting."""
    for row_index, row in enumerate(data):
        for col_index, distance in enumerate(row):
            ij = data[row_index][col_index]
            ji = data[col_index][row_index]
            if ij is None and ji is None:
                return False
            if ij != ji:
                return False
    return True
