I just checked my passport ...Here is the history..
First time entry stamping .....Jan 2011 valid till June 21011 ....during this 6 months period , visited US around 5 times ...All are days trips, was in US only few hours for shopping
Second time entry stamping ..... March 2012 ,This time officer took my previous year I-94A form and issued new one ..Its valid till sept 2012....during this 6 months period , visited US around 3 times............All are days trips, was in US only few hours for shopping
Third stamping .....October 2013, office took my previous year I-94A form and issued new one ...valid till April 2014 ( i still have form with me )...
All my visits by Car , via Vancouver border. Each visit is less than 10 hours.