I mean, that very well could happen. Porsche allowed Turn10 to model the 991 GT2 RS & debuted it at E3 alongside FM7. Then, there's the story of Turn10 getting access to the Ford GT long before its debut.
There's also the Ferrari 458 in FM3 - the car was unveiled in mid-September 2009, and the game came out at the end of October with files for the car already on the disc (as Ferrari F142, because it presumably didn't have a confirmed name yet when they started). The finished car was released in a DLC at the beginning of December, something like 12 weeks after it was first unveiled.
The McLaren MP4-12C was unveiled about the same time as the 458 and also had some parts on the FM3 disc, but wasn't released as DLC for another six months after the 458 was.