Cumulative sum with default view to show 6 months

[SaiKiran2]

I have requirement where user want to see latest 6 months data ( which should show cumulative sum from entire data set).

LOAD
    patient_id,
    Cancelled_flag,
    Date(month_year)  as month_year,
    if(isnull(month_year),null(),Month(date(month_year))&'-'&right(year(date(month_year)),2) )                 as Month_S,

FROM Table1;

//====================== Below script is for cumulative report ========================//
tmpAsOfCalendar:
Load distinct month_year 
  Resident Table1
  where month_year<>null();

Join (tmpAsOfCalendar)
Load month_year as month_year_cal
  Resident tmpAsOfCalendar ;

NoConcatenate
[As-Of Calendar]:
Load month_year,
      month_year_cal,
      if(isnull(month_year_cal),null(),
           Month(date(month_year_cal))&'-'&right(year(date(month_year_cal)),2)  )                as Month_S_cal
Resident tmpAsOfCalendar
      Where month_year_cal >= month_year;

Drop Table tmpAsOfCalendar;
//=====================================================================================
Below is the dimension and measure I have tried.

Dimension: if(GetSelectedCount(Month_S_cal)>0,Month_S_cal,
aggr(only({<[month_year_cal]={">=$(=date(monthstart(addmonths(max(date([month_year_cal])),-5))))<=$(=date(max(Date([month_year_cal]))))"}>} Month_S_cal),[month_year_cal]))
Measure: count(distinct{<[cancelled_flag]={'Y'}>}[patient_id]) 
/ Count(distinct patient_id)

I'm looking forward for suggestions to do this cumulative sum, Let me know if something is not clear!

@tresesco @sunny_talwar 

[SaiKiran2]

Using same logic, I checked for Cumulative count which is working as expected but I have an issue in calculating percentage.
Measure: count(distinct{<[cancelled_flag]={'Y'}>}[patient_id])