The issue I had was not having any items in "List X".. thus, I had nothing to update when using the "Update List Item" SharePoint 2010 Workflow Action in SPD. After adding the multiple Items, I then went back to Lists A, B, and C and updated the workflows to point to the corresponding items to update.
Questions: Which version of SharePoint are you using, Online or on-premises? Why don’t you update the SharePoint List X directly with workflow, but build the process through Excel?
SharePoint Designer (2010) workflows do not have the ability to update Excel spreadsheet. You will have to build the workflow with customization.
If you are in SharePoint ...