Just a rule to follow.
Create time dimension so that detail item iids are consistent\meaningful and then add all summary items. So then in common Months dlist you’d get 1-12 for months, 13 for “1 Quater”, 14 for “2nd Quater” and so on.
That will allow you to use simple time arithmetics in dlist formated items such as calculating previous month by – 1, not by (IF “it was the one after summ” then month_id-2 else month_id – 1) .