Since both of your datasources are coming from Excel, I'd recommend bringing them in as a single datasource in Tableau and left joining them. You won't run into blending issues that way.
Check out this article for instructions on how to join your two Excel files together, specifically the section called "Combine tables from the same database":
Thanks, Paul - maybe I could have prepared my demonstration better, but my EMR data is actually coming from a Tableau Server source which is updated daily. If I could get this calculated field to cooperate, I would set up a live connection to the Excel document updated by the Social Workers. It would be great if the users could run a report using both data sets at any time.