Renault's last visible update was this little fin behind the brake ducts. Kubica tested the two different brake ducts (square/round) with and without it...
(comparison Suzuka/Spa)
And according to Kubica (in the last podcast), his diffuser was damaged before Qualifiyng. The team tried to fix it rapidly between each Q session and the car was better in Q3... bu still with a damaged diffuser...
That means RK was never able to show the real potential of the car... He says that there was a big margin of progression after FP ... but in Qualiy the diffuser was damaged and in the race a wheel was gone...