THere's really no way to prove it wasn't there before...but, it does look different from the old paint scrape which you can see in this picture here. Look halfway between the ledge and the bottom of his bumper.
On the other side, the missing paint area is much brighter and cleaner looking.
The missing paint in that area lines up exactly with my dent. How convenient that there's missing paint on both sides!

I've now submitted this to two diferent automotive forensics labs. One here in Seattle, and one in Portland.
I told ya...I'd spend as much as it costs to make him eat it...even if I don't get that money back.

 

This may be an insignificant point, but you might be able to get the lab costs covered when you make this guy eat his words. Since he denied it right from the get-go, and still swears that he didn't do it. He has left you with no other choice to guarantee your repairs being payed for, but to prove that it was indeed his car that did the damage. This seems like the most sensible method to prove that it was indeed his car.

Given the condition of his car, and his paint job. It may work even more in your favor. I would be that it has been repainted in the past, and will probably have something rather unique about the combination of paints, such that you could prove beyond a reasonable doubt that it was his car that did the damage.
Ontop of that, if it's small claims court, it's entirely up to the judge, and it does not need to be beyond a reasonable doubt, but more about what makes the most sense. Small claims court judgements are rather subjective in that manner.

Best of luck in holding this a**hole to it!!

 

He must not be too worried he is not hassling you for taking all those pictures of his car.
Then again he could be filming you waiting for you to touch his car and then claim it was you who did all that damage to the front of his car because you were so mad about a little dent he said he would pay for.....

Too bad you could not put all the money you are going to spend towards a 951

 

So get your CSI kit back yet?

 

How do the forensics help without chain of evidence? You subitted the samples, so he could just say you took them off his car when you were measuring the impact points?

-Joel.