The OP claim did not sound right, so I fact checked. Duke has made the Sweet Sixteen 11 times in the past 16 years. The OP is full of crap. 4 times? Don't know how anyone screws up a stat that bad. Duke made the Sweet 16 in:
2002
2003
2004
2005
2006
2009
2010
2011
2013
2015
2016