After rereading the OP, it sounds like you bought the carfax report and it wasn't listed. You take it in now and the mechanic pulls the carfax report and it shows it on there now? I would find more information about that wreck. Also, a little googling comes up with this:
http://www.carfax.com/manifest/bbg/termsConditions.cfx
Did you register your report? If you did and it is less than 1 year later, it sounds like CarFax will buy your car.
The CarFax guarantee only covers you if the DMV has recorded the vehicle as "branded". This means a designation has been made by the DMV on the title stating that it was salvaged, etc. A wreck where the car wasn't totalled generally isn't enough for a DMV to label the title as branded - it's got to be something pretty major.
I'm 99% sure the title wouldn't be branded in this case. That data is easy for CarFax to pull properly.
(I deal with car titles, DMVs and their data all day long at my job.)