SAMEPERIODLASTYEAR is not working on previous year

[Anonymous]

Dears,

Here, I face a quesion that has been borthering me for several days.

First, below figure is my modeling relationship(1 is Fact Table, 2~4 are dimension Table), I would like to do a dynamic dimension form about Current Year VS Prebious Year, 

But, the PY result aloways on the PY year Not on Current Year(By week & By Month), By day is correct, like below figure 

Dex: 

SO qty = CALCULATE(

             SUM('EL SO Report'[SO qty]))

SO qty LY = CALCULATE(

                [SO qty],  

                SAMEPERIODLASTYEAR('Filter Date'[Document Date]))

I guess mybe this mapping relationship affect my Dex, but I DON'T have any better choice,hope someone could help me to identify this problem, thanks!

[lbendlin]

Time Intelligence functions like SAMEPERIODLASTYEAR expect a calendar table that is contiguous and covering (including the result of the computation)