=IFERROR(IF(INDEX('[Spreadsheet A]Sheet1'!P:P,MATCH(A2,'[Spreadsheet A]Sheet1'!A:A,0))=X2,"Matches","Doesn't match"),"Not found")
The problem is that usernames do not appear on the same number as the other spreadsheet, this is why its a pain.It doesn't matter whether you use an Excel formula, Power Query, Access, or Python--there needs to be some way of linking at least a portion of the records in one table with those in the other. You may then use that linkage method to separate your data into records that Match, those that Don't Match, and those that aren't found in the other table.