DLC cars are:
Audi R18 Audi Team Sport Joest 2016 - New
Chevrolet Corvette Stingray Convertible (C3) 1969 - GT6
Dodge Viper GTS 2002 - GT6
Ferrari 330 P4 1967 - GT6
Ferrari 512BB 1976 - GT6
Ferrari Enzo Ferrari 2002 - GT6
Ferrari F40 1992 - GT6
Ford GT 2006 - GT6
Ford F-150 SVT Raptor 2011 - New
Gran Turismo Chris Holstrom Concepts 1967 Chevy Nova 2013 - New
Jaguar XJ13 1966 - GT6
KTM X-BOW R 2012 - GT6
Lamborghini Diablo GT 2000 - GT6
Lamborghini Countach LP400 1974 - GT6
Mazda RX-7 Spirit R Type A (FD) 2002 - GT6
McLaren F1 1994 - GT6
Nissan Skyline GT-R V-spec II (R32) 1994 - GT6
Nissan Skyline GT-R V-spec II Nür (R34) 2002 - GT6
Shelby Cobra 427 1966 - GT6
Suzuki Swift Sport 2007 - GT6
Toyota 2000GT 1967 - GT6*
Toyota FT-1 - GT6
Toyota Supra RZ 1997 - GT6*
Volkswagen Sambabus Typ 2 (T1) 1962 - GT6
Zagato IsoRivolta Vision GT- New
So yes, of the 25, only 4 are new to the series. The two Toyotas marked are cars that were previously in GT5/6 but as Standard models only, so you could make an argument that they're new, but most people probably wouldn't.