Oh, wow...I know so many!!! I've always had positive HPTs, but I know that my aunt never did, 2 of my friends NEVER got one (even much later!), and several other relatives and friends missed their BFPs at home. It's not as uncommon as you'd think.
12 days late is pretty late--I'm glad you made the appointment. I hope that you get a positive result!!! That would be a GREAT reason to be so late!!! GOOD LUCK!