Migrating only articles with a specific taxonomy term
Besides setting up a process plugin for the migrate import mapping (via code) as suggested by Berdir in the comments, another option is to setup a views data export on the legacy site to output only the select articles or "interviews".  

This approach also allows non-database admins or developers to easily audit the content being migrated (because you can setup an alternative view display as a webpage, or excel spreadsheet, for use as a checklist).

To setup a view in JSON format:


install the Views Data Export module 
install one of the add-on modules for JSON, such as Services Views or Views Data Source.  


Refer to this StackOverflow answer/post about setting up a JSON view display mode.