Viewing previous version does not show previous version accurately

### Problem

Sometimes I need to view the edit history of a record to see what changes were made and when. I count on the preview of the previous version to show me accurate information. Instead, the preview of a previous version shows changes that had not yet been made making it appear as though that data existed prior to the edit I'm reviewing.

#### Evidence / Screenshot
Diff view

Preview of v. 1

Actual v. 1

#### Relevant URL(s)
https://openlibrary.org/books/OL49822191M/Poesie?m=history

### Reproducing the bug

1. Go to ...a record that has been changed incorrectly and does not have an accurate preview of previous versions.
2. Do ... see the inaccuracies as noted in the above example.

* Expected behavior: The version preview should display the previous version accurately.
* Actual behavior: It does not.

### Context

- Browser (Chrome, Safari, Firefox, etc):
- OS (Windows, Mac, etc):
- Logged in (Y/N): Y
- Environment (prod, dev, local): prod

### Notes from this Issue's Lead

#### Proposal & constraints

#### Related files

#### Stakeholders

@scottbarnes