I don't understand this part
within the last 3 years of 1/31/2015
Any how here something :
CASE WHEN DATEADD(YEAR,-3,GETDATE())< [Board Approved Date]
AND [Board Approved Date] < GETDATE() THEN 'Y'
END as result
DATEADD(YEAR,-3,GETDATE()) will return
01/12/2014 18:46:14 = last 3 year from present.
If you want from 1/31/2015 , you can replace GETDATE with your value