Changing Column values with VB code

I dont understand vb at all apparently....

ok this code works:

 For i = 1 To 18
            iRow = .Cells(Rows.Count, 1).End(xlUp).Row + 1
            .Cells(iRow, 1).Value = Me.txtDate.Value
            .Cells(iRow, 2).Value = i
            .Cells(iRow, 4).Value = Me("TextBox" & i).Value
        Next i

And in column B it displays "1" in b2, "2" in b3, "3" in b4, etc all the way to "18" in b19...
I guess that makes sense...
but what I want is to say: "51" in b2, "52" in b3, "53" in b4, all the way to "67" in b18, but in b19, I want it to say "73",

so I change the code to say:

 For i = 51 To 68           
 iRow = .Cells(Rows.Count, 1).End(xlUp).Row + 1
            .Cells(iRow, 1).Value = Me.txtDate.Value
            .Cells(iRow, 2).Value = i
            .Cells(iRow, 4).Value = Me("TextBox" & i).Value
        Next i

OK, I know I know, I did not address the "73" in b19, but I just wanted to tackle the 51 - 67 issue first, well when I change the code, it says "Object not found"...
what am I doing wrong???

Attached a workbook, you are looking at the "Order Log", sample of desired results highlighted in yellow