question about website generating a coupon code- why wont it generate another code after I clear my cookies?

Hi, I go to the website sears.com on internet explorer and scroll down a bit and I click the box that says "$10 off $40 coupon" and it generates a coupon code (I will call this coupon code a) . I printed the coupon then closed the page out and re opened IE and cleared my tracking cookies and history. I rebooted the computer and then went back to sears.com on IE and then clicked the coupon again, but it generated the same coupon code as last time (coupon code a)

So I try it on firefox and then it generates a different code (coupon code b) I cleared the cookies in firefox and tyry it again, and it generates coupon code b once again.

I then try it on google chrome and used the incognito option. This time it generated coupon code C. I clear the cookies and reboot the computer. I then open chrome again and open a new incognito window and go to sears.com again but it still generates coupon code C.

Then just to try once more I went to sears.com on IE once again just to test it once more and sure enough it still generates coupon code a.

It only generates a new code when I use a different browser.So I am wondering why clearing my cookies is not generatring a new code?