ASO OTL Formula Question

Question

I am attempting to create a scenario that presents lagged data (ie in march show the data for February). Sample of formula.
CASE
WHEN IS ([Jan],[Time].CurrentMember)
THEN ( ([Dec],[2008 Actual]))
WHEN IS ([Feb],[Time].CurrentMember)
THEN ( ([Jan],[2009 Actual]))
WHEN IS ([Mar],[Time].CurrentMember)
THEN ( ([Feb],[2009 Actual]))
WHEN IS ([Apr],[Time].CurrentMember)
THEN ( ([Mar],[2009 Actual]))
WHEN IS ([May],[Time].CurrentMember)
THEN ( ([Apr],[2009 Actual]))
WHEN IS ([Jun],[Time].CurrentMember)
THEN ( ([May],[2009 Actual]))
WHEN IS ([Jul],[Time].CurrentMember)
THEN ( ([Jun],[2009 Actual]))
WHEN IS ([Aug],[Time].CurrentMember)
THEN ( ([Jul],[2009 Actual]))
WHEN IS ([Sep],[Time].CurrentMember)
THEN ( ([Aug],[2009 Actual]))
WHEN IS ([Oct],[Time].CurrentMember)
THEN ( ([Sep],[2009 Actual]))
WHEN IS ([Nov],[Time].CurrentMember)
THEN ( ([Oct],[2009 Actual]))
WHEN IS ([Dec],[Time].CurrentMember)
THEN ( ([Nov],[2009 Actual]))
END

Answer 1

Question 1: Is there a problem with what you have? Does it work? Is it slow? are you looking to do it better?
Question 2: Do you have Year and Scenario in the Same dimension? If you do, you should change that and break them out, that is not a good design methodology
If they were separate you could do something simple like
CASE
WHEN IS ([Time].CurrentMember, [Jan])
THEN ([Actual], [Dec], [Year].CurrentMember.lag(1))
ELSE ([Actual], [Time].CurrentMember.lag(1)
END