Modify YoY% quick measure to filter data points in the future

The quick measure YoY% is giving me results for the future 12 months.  I want the YoY% to only match the dates for which there is data (Purchases).  My data ends in 12/2017 and I want the YoY% to stop on 12/2017.  

Purchases YoY% =
IF(
ISFILTERED('qCalendar'[FirstDayofMonth]),
ERROR("Time intelligence quick measures can only be grouped or filtered by the Power BI-provided date hierarchy or primary date column."),
CALCULATE(
SUM('qPurchaseHistory'[Purchases]),
DATEADD('qCalendar'[FirstDayofMonth].[Date], -1, YEAR)
)
)

Thanks in advance.