Manipulate dataset in a quarterly format

Dear All,

I am new VBA user and I would like your help because I am getting crazy. I am using a data set with 2 columns. In the first one I have the years (1970-2013) and in the second column the month of an event. What I am trying to do is to manipulate these two columns and create a third one collecting the number of these events in a quarterly form. For the quarters that no event has been occurred I just put a 0 for them.

The problem is that my code is working fine until it meets a missing year. There is something wrong and I CANT SEE IT. Can anyone help me with it please?? I have attached my data set. Much appreciated.

Sub Number_of_Crisis()

With ActiveSheet
    lastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
End With

Dat = 1970
g = 1

For p = 1 To lastRow

If Cells(p, 1) = Dat Then
     Cells(g, 4).Name = "Quarter1"
     Cells(g + 1, 4).Name = "Quarter2"
     Cells(g + 2, 4).Name = "Quarter3"
     Cells(g + 3, 4).Name = "Quarter4"
     
     If Cells(p, 2) <= 3 Then
       Range("Quarter1").Value = Range("Quarter1").Value + 1
      ElseIf Cells(p, 2) > 3 And Cells(p, 2) < 7 Then
       Range("Quarter2").Value = Range("Quarter2").Value + 1
      ElseIf Cells(p, 2) > 6 And Cells(p, 2) < 10 Then
       Range("Quarter3").Value = Range("Quarter3").Value + 1
      ElseIf Cells(p, 2) > 9 And Cells(p, 2) < 13 Then
       Range("Quarter4").Value = Range("Quarter4").Value + 1
     End If
   
ElseIf Cells(p, 1) = Dat + 1 Then
      Dat = Dat + 1
      g = g + 4
      Cells(g, 4).Name = "Quarter1"
      Cells(g + 1, 4).Name = "Quarter2"
      Cells(g + 2, 4).Name = "Quarter3"
      Cells(g + 3, 4).Name = "Quarter4"
      
     If Cells(p, 2) <= 3 Then
       Range("Quarter1").Value = Range("Quarter1").Value + 1
     ElseIf Cells(p, 2) > 3 And Cells(p, 2) < 7 Then
       Range("Quarter2").Value = Range("Quarter2").Value + 1
     ElseIf Cells(p, 2) > 6 And Cells(p, 2) < 10 Then
       Range("Quarter3").Value = Range("Quarter3").Value + 1
     ElseIf Cells(p, 2) > 9 And Cells(p, 2) < 13 Then
       Range("Quarter4").Value = Range("Quarter4").Value + 1
     End If
     
ElseIf Cells(p, 1) <> Dat Then
     Dat = Dat + 1
     g = g + 4
     Cells(g, 4).Name = "Quarter1"
     Cells(g + 1, 4).Name = "Quarter2"
     Cells(g + 2, 4).Name = "Quarter3"
     Cells(g + 3, 4).Name = "Quarter4"
     
End If

Next p

telas = (Dat - 1970 + 1) * 4

For tel = 1 To telas
  If Cells(tel, 4) = "" Then
     Cells(tel, 4) = 0
  End If
Next tel
  
End Sub