I’ve heard from people who were unable to get their stamps because the total was zero (think Ken’s dressing or the Kraft cheese deal) after coupons but before tax.  This seems to be a glitch in the registers, so make sure you keep your receipts and head over to CS and have them issue the stamps.  One reader was told that she was not owed stamps “Since you used coupons.”  Which, as we all know, is the fallback line of the Stupids.  Since the cashiers initial each redeemed receipt, an unmarked receipt should be proof enough for CS.