=IFNA(VLOOKUP(A2,'売上'!$A$2:$E$7,5,FALSE),"未登録")

=XLOOKUP(A2,'売上'!$A$2:$A$7,'売上'!$E$2:$E$7,"未登録",0,1)

=COUNTIF('売上'!$A$2:$A$7,A2)
