def clean_game_date(season_year: int, date: str) -> str:
    """Creates a date string from a season year and date string.

    Args:
        season_year (int): The season year.
        date (str): The date string.

    Returns:
        str: The date string if the date is part of the regular season, otherwise
            returns 'non-regular-season'.
    """
    if len(date) == 3 and date[0] == "9":
        return f"{season_year}-09-{date[1:]}"
    elif len(date) == 4 and int(date[:2]) > 9:
        return f"{season_year}-{date[:2]}-{date[2:]}"
    elif len(date) == 3 and date[0] in ["1", "2"]:
        season_year += 1
        return f"{season_year}-0{date[0]}-{date[1:]}"
    else:
        return "non-regular-season"