Vba to generate Reference Number, input box for user to enter 1st Ref

Hi, i have a data sheet where Column A is the Type, basically there are 3 type. A B C.
My ref is like this "A20180601" where A is the brand, 201806 is yyyymm and 01 is the number of A.
Upon clicking a button, I hope to have a inputbox where user can enter the yyyymm and the reference will automatically generate.
However, the code will prompt a input box, example "Please input the first number for Type A/B/C", when it hit the 1st A/B/C while going down the loop.
After which, it will continue to generate the Refenence number Until it reach another 1st A/B/C where it will prompt again
I need the 1st number to be manually input becoz the whole data does not come from 1 excel file and hence the 1st reference number might not be 1.

You refer to try

PHP Code: 

Option Explicit
Public Const fYear As Long = 1950
Public Const eYear As Long = 2028
    Sub pInput()
    Dim Rng_Data As Range, tDate As String, eRng As Range
    Dim N As Long, I As Long, Arr(), Txt As String
On Error GoTo Thoat
Set Rng_Data = Application.InputBox(Prompt:="Select data ", Title:="Select the data area", Type:=8)
tDate = Application.InputBox(Prompt:="Type dd/mm/yyyy ", Title:="Select dates", Type:=2)
If IsDate(tDate) = False Then
    MsgBox "Type: dd/mm/yy hoac dd-mm-yy", vbExclamation
End If
If Format(tDate, "yyyy") < fYear Or Format(tDate, "yyyy") > eYear Then
    MsgBox "No this year", vbExclamation
End If
If IsDate(tDate) = True Then
    Txt = Format(tDate, "yyyy") & Format(tDate, "mm")
End If
If Rng_Data.Columns.Count = 1 Then
    ReDim Arr(1 To Rng_Data.Rows.Count, 1 To 1)
    For I = 1 To Rng_Data.Rows.Count
        N = Application.CountIf(Range(Rng_Data(1), Rng_Data(I)), Rng_Data(I))
        Arr(I, 1) = Rng_Data(I) & Txt & Format(N, "0#")
    Next I
End If
Set eRng = Application.InputBox(Prompt:="Select a cell ", Title:="Output data", Type:=8)
eRng.Resize(I - 1) = Arr
Thoat:
End Sub