Using SWITCH or IF for parameters required for the table in DAX Filter

I have the following two examples of Calculations using a FilteredDates VAR in my Measures for a FILTER

The only difference is what I am passing to the filter

ie for Week TY I am passing
ALL(DATES),  DATES[Week] = Reporting_Week_TY   &&  DATES[Year] = Reporting_Year_TY

and for Period TY I am passing

ALL(DATES),    DATES[Week] <= Reporting_Week_TY   &&   DATES[Period] = Reporting_Period   &&  DATES[Year] = Reporting_Year_TY

ie

// Example of Week TY
// ***************************************************
// // The Calc bit :

VAR FilteredDates =

FILTER(  ALL(DATES), DATES[Week] = Reporting_Week_TY   &&    DATES[Year] = Reporting_Year_TY )

VAR HoldCalc =  SUMX(FilteredDates, [Sales])

RETURN
IF( HoldCalc = BLANK(), 0, HoldCalc )

// Example of Period TY
// ***************************************************
// // The Calc bit :

VAR FilteredDates =
FILTER( ALL(DATES), DATES[Week] <= Reporting_Week_TY &&  DATES[Period] = Reporting_Period && DATES[Year] =  Reporting_Year_TY)

VAR HoldCalc = SUMX(FilteredDates, [Sales])

RETURN
IF( HoldCalc = BLANK(), 0, HoldCalc)

All VAR etc happily predined.  Both meaures work quite fine in isolation

//*******************

I have various other calculations and the only difference is the dates being passed to the filter.   

**  All work.  ** 

Because I want to do many more measures, ie whether I am doing Sales Week TY or Profit Period LY - for example - typos will probably occur.

What I was wondering if I could have a VAR for Calcs_Needed such as

Calcs_Needed = "Week TY"
Calcs_Needed = "Week LY"
Calcs_Needed = "Period TY"

etc  (Very obviously one at a time, at the top of the code)

and THEN have a Switch or an IF in the VAR FilteredDates and put the Filter for each in. That way I change what I need at the very top of my Code and it determines what is passed to the SUMX(FilteredDates,

I tried a very basic test with

VAR FilteredDates =

IF ( Calcs_Needed = "Week TY",
      FILTER(  ALL(DATES), DATES[Week] = Reporting_Week_TY   &&    DATES[Year] = Reporting_Year_TY ),
      FILTER(  ALL(DATES), DATES[Week] = Reporting_Week_LY   &&    DATES[Year] = Reporting_Year_LY )
)

VAR HoldCalc = SUMX(FilteredDates, [Sales])

RETURN
IF( HoldCalc = BLANK(), 0, HoldCalc)

and a SWITCH version.

Both gave error  at the SUMX(FilteredDates

The expression refers to multiple columns. Multiple columns cannot be converted to a scalar value.

I thought it would be a breeze and I would longer term - having taken the 'hit' of retrofitting my code - make things much more manageable

I presume I am being very naiive thinking it would work