### Discussed in https://github.com/apache/airflow/discussions/33345

<div type='discussions-op-text'>

<sup>Originally posted by **vuphamcs** August 11, 2023</sup>
### Description

Is there a variable similar to `prev_start_date_success` but for the previous DAG run’s completion date? The value I’m hoping to retrieve to use within the next DAG run is `2023-08-10 16:04:30`

![image](https://github.com/apache/airflow/assets/1600760/9e2af349-4c3e-47e1-8a1a-9d8827b56f57)


### Use case/motivation

One particular use case is to help guarantee that the next DAG run only queries data that was inserted during the existing DAG run, and not the past DAG run.

```python
prev_ts = context['prev_end_date_success']

sql = f"SELECT * FROM results WHERE created_at > {context['prev_end_date_success']}"
```

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
</div>
"""Helper to ensure a valid virtual environment is set up and will create inplace."""
        cache_hash, hash_data = self._calculate_cache_hash()
        venv_path = venv_cache_path / f"venv-{cache_hash}"
        self.log.info("Python virtual environment will be cached in %s", venv_path)
        venv_path.parent.mkdir(parents=True, exist_ok=True)
        with open(f"{venv_path}.lock", "w") as f:
            
            fcntl.flock(f, fcntl.LOCK_EX)
            hash_marker = venv_path / "install_complete_marker.json"
            try:
                if venv_path.exists():
                    if hash_marker.exists():
                        previous_hash_data = hash_marker.read_text(encoding="utf8")
                        if previous_hash_data == hash_data:
                            self.log.info("Re-using cached Python virtual environment in %s", venv_path)
                            return venv_path
                        self.log.error(
                            "Unicorn alert: Found a previous virtual environment in %s "
                            "with the same hash but different parameters. Previous setup: '%s' / "
                            "Requested venv setup: '%s'. Please report a bug to airflow!",
                            venv_path,
                            previous_hash_data,
                            hash_data,
                        )
                    else:
                        self.log.warning(
                            "Found a previous (probably partial installed) virtual environment in %s, "
                            "deleting and re-creating.",