Dax allexcept

I've been trying to use allexcept , and failing,


I have a measure for Monthly average by year ;

AVERAGEX(VALUES('Calendar'[MMM-YYYY]),[Tunits])

Which Have then used in two version to get rolling average

  YTD avg:=CALCULATE([MonthAvg],DATESYTD('Calendar'[Date]) )

and

                        CALC Rolling Avg:=VAR  mdate = MAX('Calendar'[Date]) 
                                                             RETURN 
                                                        CALCULATE([MonthAvg],
                                                              FILTER(CROSSJOIN(ALL('Calendar'[Date]),VALUES('Calendar'[Year])),
                                                                        'Calendar'[Date]<=mdate)
                                                                             )

Rather than using CROSSJOIN ALL and VALUES, could I use ALLEXCPT instead? and if so how?

Richard