Function parse_timestamptz_legacy 

pub fn parse_timestamptz_legacy(
    s: &str,
) -> Result<CheckedTimestamp<DateTime<Utc>>, ParseError>

Parses a DateTime<Utc> from s with the frozen legacy year-month-day interpretation of ambiguous dates.

NOTE: This exists solely to keep the storage source cast CastStringToTimestampTz evaluation-stable across releases (see the stability contract in mz_storage_types::sources::casts). Use parse_timestamptz everywhere else.