multiple input source with same name & different event class while creating mapping set

Summary: While creating mapping set in cost management we can find multiple input sources with same name but different event class. How to know which one to select? for example I need a input source for "Costing Category Identified" I can find multiple input source by name "Costing Category Attribute 1" linked with different event class like PO delivery into inventory, WIP variance, Global Procurement etc. Please refer the screen shot.

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