Year formula - dynamically changing

Perhaps:

Measure = 
  VAR __Year = YEAR(TODAY())
RETURN
  SUMX(FILTER('Table',YEAR([Date]) = __Year - 1),[Column])

In case you calendar end in the same year or date is selected

Last YTD complete Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD(ENDOFYEAR(dateadd('Date'[Date],-1,Year)),"12/31"))

Measure =

var _max = year(Today())-1

Return

CALCULATE(SUM(Sales[Sales Amount]), Year(Sales[Sales date]) =_max)

or

Measure =

var _max = year(Today())-1

Return

CALCULATE(SUM(Sales[Sales Amount]), Year(Date[Date]) =_max)