regarding showing all months till the month selected can be achieved using set analysis.
ex: sum({<Maand={'<=$(=max(Maand))'}>}Data)
i believe you wanted to show all expressions and for the months and drilldown to work ? i doubt that can be done using a group and also with multiple expressions with 3 dimensions
use multiple dimensions (Maand, Person,CostProfit) instead of a group but you can't get the result when you have more than 1 expression with 3 dimensions .. if you go with one expression you can use conditional dimensions to mimic the drill down (ex: getselectedcount(Maand)=1 for Person dimension)
or wanted to include the data for all months till selected month for a drilldown dimension (ex: person) - which can be achieved using that set and group ???
