Date Diff in SQL

Year - CAST(CAST(Year(SomeDate) as char(4)) + '0101' as date)

What's the logic for PYTD?  That can wildly differ from place to place, so check out my article SQL Server Calendar Table which gives you code and a demo on how to pull this off to handle custom periods.

For Prior Year I have to include all the dates greater than 1/1/2015.  (Current year - 1).

In access this worked:  > CDate("1/1/" & Year(Now())-1

datediff (year,1,getdate ())
That gives you the number of years from 1901 until this year

Now add that to "year zero" (1900)

dateadd (year, datediff (year,1,getdate ()) ,0)

Which will return a datetime value of:
Jan 1 last year

This only returned greater than 1/1/2016, I need for this query to run and by default always go back 1 year, YTD starting at the beginning of the year.  

When I write the where statement like this, I only get > 1/1/2016.
WHERE dbo.VW_Tableau_Sell_Out.[WEEK] > dateadd (year, datediff (year,1,getdate ()) ,0)

If today were 7/19/2017, then the query should return > 1/1/2016, we are trying to automate this. Access cannot work any longer the data pulls are too large.
This worked in Access: WHERE (dbo_VW_Tableau_Sell_Out.WEEK)>CDate("1/1/" & Year(Now())-1)

Thank you!