I am pretty sure lonewolf is 100% right that the car ad question is a past one, not from this exam. The question you describe is just like the one he posted and I'm 100% positive that car ad question was NOT on the exam I took last Saturday. I've recognized every other LR that's been posted as being on my exam, but I am positive that car ad one wasn't.
Your statement contains the assumption that this question was not on an experimental LR section 
No. I stated MY exam. It was not on my exam and is therefore not the missing 50th question. Wasn't on my LR experimental either though, but either way, it cannot be the missing question because if it was, it would have HAD to have been on my exam.
There are sometimes more than one experimental LR section - it was certainly the case in December. Search old posts if you don't believe me, but it's true.
You said "it cannot be the missing question because if it was, it would have HAD to have been on my exam" - if you and I had a different LR experimental, and it was on mine and not yours, then the question was indeed on
this exam, just on your version of it.
LOL. I really should be working instead