It seems very much to depend where in the world you are.
I've seen evidence for the AE vouchers having only 20 cars and evidence of vouchers that give 25.
I've seen pictures of the vouchers that give 25 cars and it actually stats "25 cars" in print (the Canadian AE [due to English/French texts on packaging] seems to have a 25 car voucher.
I have not yet seen a picture of what the voucher says in print form for people who have received only 20 cars. People who say that they only got 20 cars never quote from the voucher.
There really needs to be a Universal thread or place where each region can post pictures of the vouchers and or receipt printed codes [without showing the actual code itself of course].
It's become very clear that there are always people having trouble getting all the DLC they were promised from their pre-orders and this is because different regions do it differently. I wish that Sony or whoever determines DLC would find a way to create a universal system that the actual sellers of the products had no problem understanding; there really is no excuse when one company (GameStop/EBGames) is supposed to give exactly 25 cars to every AE pre-order in the world but they cannot figure out how to achieve it.
And yet I've read posts where in some places in the world other retailers also have been selling AE copies [In Canada and possibly all of NA only GS / EBGames were supposed to sell pre-order AE; I say pre-order because it wouldn't surprise me if the AE became sold everywhere at a later stage.]. The system of DLC pre-orders is a mess and the creators, advertisers, and the sellers all seem to have been making a bigger and bigger mess of it over the years. It really should not be the buyer's responsibility to ensure they get everything they were promised and paid for...should it?