Last 5 Weeks

Hi Xandman 

From your statement, I know you want to show Flags like PW,PW1 for previous months instead of only weeknum.

From your code, I know you have two tables, date and completework tables. 

Completework table is your data table. Here I build a sample.

I think you need to build a date table and add a custom weeknum column and year column in it by dax. If you use weeknum function directly, you will get wrong weeknum at the end of the previous year and the beginning of the next year.

For example: 

In my Sample I let week start on Sunday.

2020/12/31,2021/01/01,2021/01/02 are in the same weeknum, but weeknum function will give you 53 in 2020 and 1 in 2021. It's wrong result.

Firstly build a calendar table by dax and add calculated columns in it to get correct weeknum ,year and rank.

Date = 
ADDCOLUMNS (
    CALENDAR ( DATE ( 2019, 01, 01 ), DATE ( 2021, 12, 31 ) ),
    "Year", YEAR ( [Date] ),
    "Month", MONTH ( [Date] ),
    "WeekNum", WEEKNUM ( [Date], 1 ),
    "WeekDay", WEEKDAY ( [Date], 1 ),
    "MonthName", FORMAT ( [Date], "MMMM" ),
    "DayName", FORMAT ( [Date], "DDDD" )
)

Calculate columns:

ISO 8601 WeekNum = 
VAR _COUNT0 =
    CALCULATE (
        COUNTROWS ( 'Date' ),
        FILTER (
            'Date',
            'Date'[Year] = EARLIER ( 'Date'[Year] )
                && 'Date'[WeekNum] - 1 = 0
        )
    )
VAR _BASENUM1 =
    IF ( _COUNT0 < 7, 'Date'[WeekNum] - 1, 'Date'[WeekNum] )
VAR _ISO_8601_WeekNum =
    IF (
        WEEKDAY ( DATE ( 'Date'[Year] - 1, 01, 01 ) ) <> 1
            && 'Date'[Year] = 'Date'[Year]
            && _BASENUM1 = 0,
        WEEKNUM ( DATE ( MIN ( 'Date'[Year] ), 12, 31 ), 1 ) - 1,
        _BASENUM1
    )
RETURN
    _ISO_8601_WeekNum

WeekYear = 
VAR _COUNT0 =
    CALCULATE (
        COUNTROWS ( 'Date' ),
        FILTER (
            'Date',
            'Date'[Year] = EARLIER ( 'Date'[Year] )
                && 'Date'[WeekNum] - 1 = 0
        )
    )
VAR _BASENUM1 =
    IF ( _COUNT0 < 7, 'Date'[WeekNum] - 1, 'Date'[WeekNum] )
RETURN
IF(_BASENUM1 = 0,'Date'[Year] -1,'Date'[Year])

YearWeekRank = RANKX('Date','Date'[WeekYear]*100+'Date'[ISO 8601 WeekNum],,ASC,Dense)

PW Flag =
VAR _CurrentRank =
    CALCULATE (
        MAX ( 'Date'[YearWeekRank] ),
        FILTER ( 'Date', 'Date'[Date] = TODAY () )
    )
RETURN
    SWITCH (
        TRUE (),
        'Date'[YearWeekRank] = _CurrentRank - 1, "PW",
        'Date'[YearWeekRank] = _CurrentRank - 2, "PW2",
        'Date'[YearWeekRank] = _CurrentRank - 3, "PW3",
        'Date'[YearWeekRank] = _CurrentRank - 4, "PW4",
        'Date'[YearWeekRank] = _CurrentRank - 5, "PW5",
        BLANK ()
    )

 Date table will look as below.

Then relate completework table and this date table by date columns.

Build measures as below.

TotalWork = CALCULATE(DISTINCTCOUNT(CompletedWork[W#]),FILTER('Date','Date'[PW Flag]<>BLANK()))

Count Previous Week = SUMX('Date',[TotalWork])

Build a matrix and result is as below.

Best Regards,
Rico Zhou

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.