creating a revision report

if the users are using the form normally, you can set up a few dynamic form rules to create a time-stamp when those field in question are changed.

If you want more reporting to see not only when it changed, but who, is you can do a few things.

If it is a text field, you can turn on 'edit logging'

If it is a date field then you can set up a date change table.  The user will click a button, add a new date, and possibly enter their 'reason'.

Then you can summarize the most recent data change back to the parent, along with when it was changed.

Most people like this approach when they have dates that change often because of outside factors.