I have a data source where I link two tables with a left outer join. The issue, is when a record is not in the other table, it is not appearing in my tableau

I just performed the join using the csv files and, when I view it, I don't see those two at all.

The reason for this is that you're using Nombre Empleado on this sheet, but those don't exist in that sheet--so there's nothing to show--they'll be lumped into NULL. You can see this if you add NRO Leg to the view.