### 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>
another_task(inp, val)  # val here should resolve to [2, 4, 6].
            tg2.expand(inp=["a", "b"])
        The surrounding mapped task groups of ``upstream`` and ``self.task`` are
        inspected to find a common "ancestor". If such an ancestor is found,
        we need to return specific map indexes to pull a partial value from
        upstream XCom.
        :param upstream: The referenced upstream task.
        :param ti_count: The total count of task instance this task was expanded
            by the scheduler, i.e. ``expanded_ti_count`` in the template context.
        :return: Specific map index or map indexes to pull, or ``None`` if we
            want to "whole" return value (i.e. no mapped task groups involved).
        """
        
        
        
        
        
        if not ti_count:
            return None
        
        
        
        
        common_ancestor = _find_common_ancestor_mapped_group(self.task, upstream)
        if common_ancestor is None:
            return None
        
        
        
        ancestor_ti_count = common_ancestor.get_mapped_ti_count(self.run_id, session=session)