Percent of difference with dynamic dates and drillthrough

Hi All

Help is needed. 

(for some reason all tables i post from excel are shown here from right to left , while they shoud be left to right - probably due to hebrew -english copy paste problems ... please note)

I want to show on a visual matrix the difference between number of registrants between all the dates the user selected in the slicer (meaning dynamic date filter) - if I have 3 dates: 1.1.2018 ; 1.5.2018 and 1.10.2018 I want to show the difference between 1: 1.5.2018 to 1.1.2018 and between 1.10.2018 to 1.5.2018.

I successfully managed to do this using the following DAX code: (when MyTable is the data table , Reg includes the number of registrants  and date hold the date. please note that dates can be any date and not a day before or month before etc. ...)

% registrants =

VAR previousDate =

    CALCULATE (

        MAX ( MyTable[Date] ),

        FILTER ( ALLSELECTED ( MyTable), MyTable[Reg] > 0 &&  MyTable[Date]< MAX ( MyTable[Date] ) )

    )

VAR previousREG =

    CALCULATE (

        SUM ( MyTable[Reg] ),

       FILTER ( ALLSELECTED( MyTable) ,  MyTable[Date]= previousDate )

    )

RETURN

           DIVIDE( SUM ( MyTable[Reg] ) -previousReg,previousReg,0)

 on the following dataset : 

Up until this point all goes well - superb!  I get something like this (I put this table in excel to avoid starting to translate my entire dataset):

However , I want to add to my matrix the ability to drill through / expend to the levels of the following Hierarchy: 
this also work if I enable the user to filter the school , faculty , or section using a slicer

***PROBLEM starts here ***

1. Section 
2. Faculty 
3. School

it seems the drill through are not influence the ALLSELECTED dax statements. let say no filter were applied  I get the following visual:

calculation made by power bi is actually (40-192)/192 instead of (40-70)/70 , because the VAR previousREG for some reason is not filtered by the drill through/expend I made. 

so my question really is  -  can a drill through filter can applied and change this DAX code correctly ? I tried to change the code and remove the ALLSELECTED statement:

VAR previousREG = CALCULATE ( SUM ( MyTable[Reg] ),
 FILTER (( MyTable) , MyTable[Date]= previousDate ) 
)

However I received blanks instead of calculation results for some reason (why is that ?)

Thanks all for reviewing and trying to help

Elad