Not answering your actual question, but ...

> However, the situation is that I set  up the SelectionChange
> event to fire  only when the user  clicked in the first column  of the
> sheet, because it make the offsets so easy  to maintain
> systematically ...

You can take control of your columns in a different way. I'm assuming that
the cell that is clicked  is called Target in your event sub. Then

Option Explicit

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim TargetRow As Integer: TargetRow = Target.Row
Cells(TargetRow, "F").Value = "xx"
End Sub

I.e. grab the row number from the target cell and use the column you want in
a cells  call. My example puts an "xx" in column F of any row you click  in.

> That way, it was only a matter of counting  the
> columns to locate  the exact position  of the data  being changed.

For my way, there's no counting at all - just use the column's letter (or
letters).

If you want a group  of adjacent cells, then something like

Range(Cells(TargetRow, "J"), Cells(TargetRow, "L")).Value = "zz"

or

Range("J" & TargetRow & ":L" & TargetRow).Value = "zz"

can be useful - and still no counting.