Incomplete data for YoY%

I encounter similar situations frequently, and my pattern is to always create a measure which I call Pivot Date. Pivot Date contains the latest date of historical data. Use whatever logic you need to arrive at this date. Then you can use a statement like  min(pivot date, max(date dimension)) to filter your dates to the proper cutoff. This will work properly for prior and current years.

Pivot Date is very handy for doing prior period to-date calculations or if you're doing forecasting and need future dates in your calendar but also need to keep track of the cutoff of historical actuals.