During debugging of https://github.com/nextstrain/augur/issues/1785, I realized that the ncov-ingest [format_date](https://github.com/nextstrain/ncov-ingest/blob/fc91ecca68c3a96239a5263b803bf1565da0e025/lib/utils/transform.py#L58) transformation does _not_ mask incomplete dates with `XX`.
During debugging of nextstrain/augur#1785, I realized that the ncov-ingest format_date transformation does not mask incomplete dates with
XX.