def get_formatted_number(num):
    """
    Get a formatted string of a number from a not-predictable-string
    that may or may not actually contain a number.
    Append a BC notation to the number num with, if the
    number is negative.
    returns: a formatted string of the number, or num if
             num is not negative or None.
    """
    if not num:
        return None
    if all(['-' in num, num.replace('-', '').strip().isdigit()]):
        return ' '.join([num, 'BC'])
    return num
