People seem to have some weird mental blank spots about wisdom tooth removal. I know one person that woke up from anesthesia and said (through a mouthful of gauze) that she couldn't go home, because her wisdom teeth hadn't been taken out yet. I know at least two people that had experiences in the first few hours that they didn't remember afterward. I know I had my own wisdom teeth removed, but I don't really remember anything about what it was like afterward.
Like you, I have a hard time believing that they were extracted with you having no memory of it at all (planning for it, recovering afterward, etc.) But I also have a hard time believing that wisdom teeth could just vanish. Or that the x-ray is wrong. So that's a real puzzle.
Can you contact your previous dentist and see if they know anything?
Check back through dental insurance and medical insurance, to see if you find anything there?
If you live with anyone (parents, spouse, roommate, etc), maybe ask them?
Is there any record of you taking time off work or school?
An old calendar with appointments written on it? Email talking about it?