Watch Events module outputting of custom fields

I'm working on a scenario with a Watch Events module--it's triggered when a custom project field (1) exists; and (2) is changed (the custom field is a date field).  I added a Set Variable module used to parse the date.  However, I've discovered that the custom field is not available in the mapping panel under the Watch Events module; instead I have to add a Read a Record module to output the custom field (and then use that in the Set Variable module).

When I look at the scenario history, the output of the Watch Events module includes all of the custom project fields and their values (under the newState collection).  Is there a reason why these fields wouldn't be available in the mapping panel of downstream modules--particularly when one of these fields is the basis for the scenario trigger?

Thanks.