Hi
Sorry I didn't see your final post where you say it's been sorted but I've written the reply so I'll post it anyway.
First off you've got to put your uncle in the frame for the time he was speeding in your car; I'm glad he's not my uncle!
Second your dealer from whom you bought the car gave you completely duff info. It's an offence not to notify DVLA when you sell a car. This happened to my mate who kept getting letters through the post about unpaid parking tickets; and the old bill calling on him about his old car leaving petrol stations without paying for petrol. He'd sold the car 8 months previously and hadn't sent his log book off.
The dealer should have sent the log book to DVLA as soon as he sold it to you. There is a section on the logbook for dealers. I think this is so that the number of previous keepers isn't increased when a dealer gets it and sticks it on a forecourt.
An N.I.P. (Notice of intended prosecution) has to be served on the registered keeper for a speeding offence within 14 days. The N.I.P. was probably served on the dealer who sold you the car or the person who he had it from. That's it; it's just a legal requirement. You got the letter late probably because the N.I.P was served on the registered keeper who bounced it back and eventually the trail lead to you.
Fight it at court and you loose; the fine is always higher. They've got the speeding offence procedures pretty sewn up because every excuse in the book has been tried. As the owner of the car you can be compelled to declare who was the driver at the time of the offence. I've heard of students selling their licences and accepting the points for you. Another mates wife took points for him because he was on 9 points and facing a ban. Get caught doing this though and you're looking at perverting the course of justice....BIG POO!
Get your uncle to do the honourable thing and accept his points.