What do you mean by RM? Besides, you most of the cars you named are different from each other. Please understand that the same name does not mean the same car. Saying "4 camries" and "2 swifts" doesnt tell the story of how different they are from one another.
5 Impalas...
102.P Chevrolet 2010 Dale Earnhardt Jr. #88 AMP Energy/National Guard CHEVROLET IMPALA ‘10
103.P Chevrolet 2010 Jeff Gordon #24 DuPont CHEVROLET IMPALA ‘10
104.P Chevrolet 2010 Jimmie Johnson #48 Lowe’s CHEVROLET IMPALA ‘10
105.P Chevrolet 2010 Juan Montoya #42 Target CHEVROLET IMPALA ‘10
106.P Chevrolet 2010 Tony Stewart #14 Office Depot/Old Spice CHEVROLET IMPALA ‘10
4 Camries...
910.P Toyota 2010 Brian Vickers #83 Red Bull TOYOTA CAMRY ‘10
911.P Toyota 2010 Denny Hamlin #11 FedEx TOYOTA CAMRY ‘10
912.P Toyota 2010 Joey Logano #20 The Home Depot TOYOTA CAMRY ‘10
913.P Toyota 2010 Kyle Busch #18 M&M’S® TOYOTA CAMRY ‘10
2 SuperGT GT-Rs
772.P Nissan XANAVI NISMO GT-R (SUPER GT) ‘08
774.P Nissan YellowHat YMS TOMICA GT-R (SUPER GT) ‘08
2 GT-R SpecVs
688.P/S Nissan GT-R SpecV ‘09
689.P Nissan GT-R SpecV (GT Academy Version) ‘09
"RM" models (I assume they are simply tuned versions of stock cars, thus "padding", could be wrong)...
7.P/S Acura NSX ‘91
8.P Acura NSX RM ‘91
111.P Chevrolet Camaro SS ‘10
112.P Chevrolet Camaro SS RM ‘10
126.P Chevrolet Corvette Z06 (C6) ‘06
127.P Chevrolet Corvette Z06 (C6) RM ‘06
129.P/S Chevrolet Corvette ZR1 (C6) ‘09
130.P Chevrolet Corvette ZR1 (C6) RM ‘09
166.P Dodge Challenger R/T ‘70
167.P Dodge Challenger R/T RM ‘70
etc etc...
So there's "NASCAR Impala" counted 5 times in the "220 premiums", hence 4 cars worth of padding. I haven't gone through them all because I'm lazy, you can see them yourself by looking at the car list and look at cars that are clearly duplicates or aren't "unique". I'm sure there's more than 28 cars worth of padding in the list, that was just from a quick glance. I dont know much about Skylines or Japanese cars in general so I dont know which would be considered padding except the blatantly obvious ones I mentioned above.