Content with confusing public_updated_at dates

[fofr]

We're moving rendering from specialist-frontend to government-frontend. As part of this we are taking a look at the most popular specialist documents, the top page is:
https://www.gov.uk/business-finance-support/start-up-loans-uk

These are the dates in the content item:

"first_published_at": "2017-03-20T10:26:36.000+00:00",
"public_updated_at": "2017-03-27T13:31:41.000+00:00",
"change_history": [
  {
    "note": "First published.",
    "public_timestamp": "2017-03-20T10:26:36.341Z"
  }
]

How that renders

This is how that renders on specialist-frontend, on live (clearly a bug):

government-frontend uses the change notes to determine the first published date and whether there have been any updates, as first_published_at is considered to be unreliable (some content items have a first published date after public_updated_at):

How has an item been publicly updated without a change note being added?

When a major update is made, ie a publicly updated one, the editor requires a change note:

cc @rubenarakelyan @tijmenb

[rubenarakelyan]

The public_updated_at dates were not initially migrated from the business-support-api, which stopped anyone from updating these documents in specialist-publisher. They were set later using the ops:set_public_updated_at rake task, which doesn't set a change note. I thought I set the date to something that made sense but apparently not. It probably makes sense to set them to the first published date since I don't think any of them have changed since migration (at least the ones without a change note).