SAMEPERIODLASTYEAR contiguous selection issue

[Jebilaya]

I have a date master table against which my SAMEPERIODLASTYEAR DAX works fine however I have another report so the user can select a rolling 12 month date range (Date Range Selection) which has a 1 - Many relationship back to the date master table.

However my sameperiod last year formula does not work when this is presented on visuals.  Any ideas?

Relationships as below:

Works fine when individual year from the date master table is selected

Does not work if rolling 12 months from date range selection is selected

Dax for LY measure is 

NMR LY = calculate([NMR], SAMEPERIODLASTYEAR('Dim Date Master'[Date]))
Dax for Date range selection is 

Date Range Selection =

Var enddate = max('Fact Safety Stats'[W/C Date])

Var startdate = enddate - 362

Var result =

union(

ADDCOLUMNS(calendar(startdate, enddate), "Selection", "Rolling 12 Months", "Order", "1"),

ADDCOLUMNS(calendar(startdate - 396, startdate - 1), "Selection", "Prior Year", "Order", "2"))

 return

 result

[lbendlin]

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