Previous Period as single Value

Hi, thank you, but I couldn't find a solution there. I tried two approaches. With ISINSCOPE it seems it does not work with an automatic hierarchy. My resultset is always empty. I used

SWITCH(TRUE,

   ISINSCOPE(Date.Day), ~Calculation for day level~

   ,ISINSCOPE(Date.Month), ~Calculation for month level~

   ,ISINSCOPE(Date.Quarter), ~Calculation for quarter level~

   ,ISINSCOPE(Date.Year), ~Calculation for year level~

The result is always empty, although i tested the calculation for month level and it is correct. But even on month level it looks like this:

The other thing I thought about is PARALLELPERIOD, but the issue with that is, that it returns a table of dates. But I need a single value to compare it to my SCD2 data. MIN(PARALLELPERIOD()) is also not possible, because MIN requires a column, not a table.