When I got my impreza I knew it was a special edition - the Terzo, meaning third, signifying the third successive win for Subaru in the WRC.
There were 333 made, numbered 1-334 (omitting 13), and each was given a special plate in the interior with the unique number, but unfortunately some time during the 110,000 life of my impreza the number got lost.
I called Subaru's tech help in the UK and spoke to someone who simply asked for the registration plate, and was able to tell me that this impreza was registered number 244. I was hoping for 252, as that is in the number place, but whatever. Finding out the number wasn't nearly as exciting as I had hoped, but its nice to know :)