For me an original car is just as it came from the factory or dealer ( dealers did add some things ) YET, I do expect a few things to have been changed, like the battery, tune up parts, tires, the basic parts that need replaced every so often, maybe even the brake shoes, BUT, the paint, interior, motor should be "ORIGINAL". Like you, I've seen the adds that say " All original , new paint, redone interior, with a 350 chevy motor ect.. " I'm thinking, well, what's original? haha. When I take my 53 Manhattan to shows, I tell people the truth, it's all original EXCEPT ( the basics tires, ect. ) one repaint in original color, and the seats were redone due to a bad tear in the drivers area. The rest of the interior is the factory "original" interior.
RESTORED as "original" has a different meaning to me, It's not the original paint or interior, but done as factory. So, I see Original and restored as original a bit different, but factory correct, I am a purist, and love the history, so I try hard to keep my cars as original as possible, This way I can share with the younger generation the way things were back then, with the correct hubcaps, ect.. I even put a "original" magazine from the same year in the front seat as well as sales brochures for the vehicle, haha But, that's just me, Good question.