Try...

Sub ReplaceMatches2()
Dim vDataSource, vDataTarget, n&

vDataSource = Sheets("Errata").Range("A2:C1711")
vDataTarget = Sheets("Data").Range("D2:D1711")

vDataSource = rngSource: vDataTarget = rngTarget

For n = LBound(vDataSource) To UBound(vDataSource)
If InStr(vDataTarget(n, 1), vDataSource(n, 1)) 0 Then _
vDataTarget(n, 1) = vDataSource(n, 3)
Next 'n
Sheets("Data").Range("D2:D1711") = vDataTarget
End Sub

--
Garry

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