November 2017 - last edited November 2017
November 2017
I think at bronze get 5 BPs and start to collect BPs from replayable races ( if you stop the event or can't go further ) the same will happening if you get silver tier and stop there. You need 35 BPs to unlock the car.... you get the car unfixed and start to upgrade it from the beginnig... I hope to help you.
December 2017
If you complete Gold tier you will not receive rewards for Silver tier. Just as you wont receive Bronze rewards if you complete the Silver tier.
Basically wherever you are at the conclusion of the event dictates the award you are given.
Think of it like the Olympics, if you win a Gold, you don't also get the Silver and Bronze medals.