Here's an alternative class that uses mouse move (some of the
improvements below can be used in class above too).
But you get some flicker if there are a lot of data points;
unfortunately it doesn't seem possible to show/hide datalabels, have
keep recreating them and each step causes a flicker.

Class
------PointMouseMoveLabeller

Option Explicit

Private WithEvents mChart As Excel.Chart

Private labels As Variant
Private prevArg1 As Long
Private prevArg2 As Long

Public Sub init(a_chart As Excel.Chart, some_labels As Variant)
Dim v As Variant
Set mChart = a_chart
labels = some_labels

mChart.ProtectGoalSeek = True
For Each v In mChart.SeriesCollection
v.HasDataLabels = False
Next
End Sub

Private Sub mChart_MouseMove(ByVal Button As Long, ByVal Shift As
Long, ByVal x As Long, ByVal y As Long)
Dim elementId As Long, arg1 As Long, arg2 As Long
mChart.GetChartElement x, y, elementId, arg1, arg2
If elementId = xlSeries Then
' Uses same label whatever the series, so don't care about
arg1 (Series#) changes.
If prevArg2 < arg2 Then ' And prevArg1 < arg1 Then
unlabelLastPoint
prevArg1 = arg1
prevArg2 = arg2
If arg2 <= UBound(labels) Then
With mChart.SeriesCollection(arg1).Points(arg2)
Application.ScreenUpdating = False
.HasDataLabel = True
.DataLabel.Font.Size = 8
.DataLabel.Text = labels(arg2)
.DataLabel.Border.Weight = xlHairline
.DataLabel.Shadow = True
.DataLabel.Interior.Color = 13434879
.DataLabel.Position = xlLabelPositionAbove
Application.ScreenUpdating = True
End With
End If
End If
Else
unlabelLastPoint
End If
End Sub

Private Sub unlabelLastPoint()
On Error GoTo sub_end
With mChart.SeriesCollection(prevArg1).Points(prevArg2)
If .HasDataLabel Then
.HasDataLabel = False
End If
End With
sub_end:
prevArg1 = 0
prevArg2 = 0
End Sub