- Create a new model
- Add data that has a table. (Don't worry, you won't execute any tools)
- Add the 'Add Fields (multiple)' tool and make the data the input table
- Create a couple of new fields (again, don't execute)
- Connect Calculate Field to the output of Add Fields and open Calculate Field
- The fields you added with Add Fields don't appear in the list of fields to calculate. They should -- that's the behavior of Add Field.
Add Fields isn't updating its output data element with the new fields.
UPDATE: I wasn't able to reproduce this after closing & reopening project, or trying this in other projects. User error?