Full volume PDFs mistakenly linked as frontmatter

### Confirm that this is a bug report

- [X] I want to report an issue that does _not_ concern paper or author metadata.
- [X] I have searched for similar existing issues first.

### Problem Description

When have we started linking full volume PDFs to frontmatter, instead of to the volume's `` block? Examples:

- https://aclanthology.org/2021.nejlt-1.0/
- https://aclanthology.org/2018.ijclclp-1.0/
- https://aclanthology.org/2019.ijclclp-1.0/
- https://aclanthology.org/2020.ijclclp-1.0/
- https://aclanthology.org/2021.ijclclp-1.0/
- https://aclanthology.org/2017.tal-1.0/
- https://aclanthology.org/2019.tal-1.0/
- https://aclanthology.org/2020.tal-1.0/
- https://aclanthology.org/2021.tal-1.0/
- ~https://aclanthology.org/2023.acl-long.0/~ (sorry, got ahead of myself here, this is correct)

IMO none of these should be ``. I feel we're doing something fundamentally wrong here?

@anthology-assist @mjpost #2679 #2478

Start by reviewing the listed volume records and comparing how their full-volume PDFs are classified relative to the and blocks. Read the discussion in issues #2679 and #2478 before deciding the intended classification; done means the affected records consistently link the PDFs to the correct block and the examples no longer reproduce the bug.

由索引模型根据 Issue 内容生成。