Cell date format in excel showing datetime - vb.net

Question

I have an application that can retrieves the install date and save it at a datagridview column with the format of date only.
But when I tried to export it to an excel file, even when I tried to format the cell, it still shows me datetime instead of date only for some of the data.
The code for exporting is shown below. btw I'm using vb.net
'reportFile : True = IE_Version_Report.xlsx False = Data.xlsx
Sub ExportData(reportFile)
Dim dSet As New DataSet
dSet.Tables.Add()
For i As Integer = 0 To DataGridView1.ColumnCount - 1
dSet.Tables(0).Columns.Add(DataGridView1.Columns(i).HeaderText)
Next
Dim dr As DataRow
For i As Integer = 0 To DataGridView1.RowCount - 1
dr = dSet.Tables(0).NewRow
For j As Integer = 0 To DataGridView1.Columns.Count - 1
dr(j) = DataGridView1.Rows(i).Cells(j).Value
Next
dSet.Tables(0).Rows.Add(dr)
Next
Dim Ex As Microsoft.Office.Interop.Excel.Application
Dim Wb As Microsoft.Office.Interop.Excel.Workbook
Dim Ws As Microsoft.Office.Interop.Excel.Worksheet
Dim misValue As Object = System.Reflection.Missing.Value
Ex = New Microsoft.Office.Interop.Excel.Application
Wb = Ex.Workbooks.Add(misValue)
Ws = Wb.Sheets("sheet1")
Dim dt As DataTable = dSet.Tables(0)
Dim col, row As Integer
Dim rawData(dt.Rows.Count, dt.Columns.Count - 1) As Object
For col = 0 To dt.Columns.Count - 1
rawData(0, col) = dt.Columns(col).ColumnName.ToUpper
Next
For col = 0 To dt.Columns.Count - 1
For row = 0 To dt.Rows.Count - 1
rawData(row + 1, col) = dt.Rows(row).ItemArray(col)
Next
Next
Dim finalColLetter As String = String.Empty
finalColLetter = ExcelColName(dt.Columns.Count)
Dim excelRange As String = String.Format("A1:{0}{1}", finalColLetter, dt.Rows.Count + 1)
Ws.Range(excelRange, Type.Missing).Value2 = rawData
Ws.Range("A1:L1").EntireColumn.AutoFit() 'columns in excel file will autofit according to the data
Dim num As Integer = DataGridView1.Rows.Count + 1
'set the format for dates in these few columns
Ws.Range("D2:D" & num).NumberFormat = "dd/mm/yyyy;#"
Ws.Range("F2:F" & num).NumberFormat = "dd/mm/yyyy;#"
Ws.Range("H2:H" & num).NumberFormat = "dd/mm/yyyy;#"
Ws.Range("J2:J" & num).NumberFormat = "dd/mm/yyyy;#"
Ws.Range("L2:L" & num).NumberFormat = "dd/mm/yyyy;#"
Ws = Nothing
If reportFile = True Then
fileExported = True
If System.IO.File.Exists(FolderPath & "\MSOffice_Report.xlsx") Then
System.IO.File.Delete(FolderPath & "\MSOffice_Report.xlsx")
End If
Wb.SaveAs(FolderPath & "\MSOffice_Report.xlsx")
Else
fileExported = False
If System.IO.File.Exists("C:\Install\MSData.xlsx") Then
System.IO.File.Delete("C:\Install\MSData.xlsx")
End If
Wb.SaveAs("C:\Install\MSData.xlsx")
SetAttr("C:\Install\MSData.xlsx", vbHidden)
End If
Wb.Close(True)
Wb = Nothing
Ex.Quit()
Ex = Nothing
GC.Collect()
End Sub
Public Function ExcelColName(ByVal Col As Integer) As String
If Col < 0 And Col > 256 Then
MsgBox("Invalid Argument", MsgBoxStyle.Critical)
Return Nothing
Exit Function
End If
Dim i As Int16
Dim r As Int16
Dim S As String
If Col <= 26 Then
S = Chr(Col + 64)
Else
r = Col Mod 26
i = System.Math.Floor(Col / 26)
If r = 0 Then
r = 26
i = i - 1
End If
S = Chr(i + 64) & Chr(r + 64)
End If
ExcelColName = S
End Function
Sorry if it's a very stupid question but I really don't know what's wrong with it.
Thanks!

Answer 1

Excel does not recognise dates earlier than 1/1/1900 and will treat a value like 11/11/1111 12:00:00 AM as text. See how the dates are right-aligned and the text is left aligned in your screenshot?
Text will not be affected by the number formatting you apply to show only the date of the values.
Depending on what you want to achieve, you need to adjust your code to handle the text values differently. Replace them with 1/1/1900 or some such.