If these are constant values (i.e. Month = 01 does not vary according to the start date of the report) then have you considered setting up an internal lookup table? To me it offers a more elegant approach fixed entities with known values. The IF() option is useful in this context where there some of the data may be of poor quality or have a value outside the regular values but if the values are almost certainly known and constant I think a lookup table is more appropriate.
Just my opinion of course.