Duplicate Columns in List Export

When exporting a list and including "Person Source" in the export, it shows 2 columns "Person Source" and "Person Source (A)". What is the difference? And why are their discrepancies between the 2?

For example, in some instances there is now Person Source, but there is a Person Source (A).

And in some records, the Person Source and Person Source (A) are different from each other.