import re


def date_to_version(tag):
    """Convert a tag from YYYYMMDD to y.M.D where y is years after 2020."""
    if re.match(r"\d\d\d\d\d\d\d\d", tag):
        year = int(tag[2:4]) - 20
        month = int(tag[4:6])
        day = int(tag[6:8])
        return f"{year}.{month}.{day}"
    return tag