Reduce Rows with Data

is expected output one very long row for each ID?
It wil be a) very tough to read b) even tougher to process

3 additional questions:
- will there be always 12 rows for each ID? or could it change - some ID's with less, or may be some with more rows?
- will start and end dates (columns B and C) have the same values within single ID?
- why do you put texts just looking as dates, not real excel dates in column B?

Don't know why you cannot answer in the thread (as you reported in PM), but the solution could be such code:

Sub collate_rows()
Dim rows_to_delete As Range, current_row As Long, previous_ID As String
Dim row_in_sequence As Long, max_row_in_sequence As Long

For current_row = Cells(Rows.Count, "A").End(xlUp).Row To 2 Step -1
  If Cells(current_row, "A") <> previous_ID Then
    row_in_sequence = 1
    previous_ID = Cells(current_row, "A")
  Else
    Cells(current_row, "T").Resize(1, 16 * row_in_sequence).Value = Cells(current_row + 1, "D").Resize(1, 16 * row_in_sequence).Value
    row_in_sequence = row_in_sequence + 1
    If row_in_sequence > max_row_in_sequence Then max_row_in_sequence = row_in_sequence
    If rows_to_delete Is Nothing Then
      Set rows_to_delete = Rows(current_row + 1)
    Else
      Set rows_to_delete = Union(rows_to_delete, Rows(current_row + 1))
    End If
  End If
Next current_row
If Not (rows_to_delete Is Nothing) Then
  rows_to_delete.Delete
  Cells(1, "D").Resize(1, 16).AutoFill Cells(1, "D").Resize(1, 16 * max_row_in_sequence)
End If
End Sub

See also attached file