I'm trying to show an example of data differences with name fields, specifically Middle name and "Nickname" (custom text field on contact record).
Two things I'm noticing:

Neither Middle name, nor "Nickname" shows up as a data difference even though there are different names on that record in SF. In the review screen, if I add the middle name and nickname fields to the Summary window in Salesforce, nothing shows in the SF record box.

When I go to my matching, I can't add additional fields to Name criteria. I also can't include these fields on Name & Address criteria.

This is causing data differences between these fields to not be displayed when selecting which fields to update in Salesforce.