Rob is correct manufactured 2000 but titled as a 2001 model though the title should have the actual date of registration on it, I haven't done one for years and DVLA always used to take the reg date from the title, though must admit they seem to be worse now than ever, even to the extent we had a guy apply for his provisional class C licence and they issued him with a full C+E he told them don't know if I would you need to ask them exactly why they wont register it if they say because its year of manufacture is unknown then Thor should be able to issue a build date for you and a dealer that it was supplied to and information gained from them DVLA wont have an argument, or you would like to think.
If you call them & IF you are very lucky & get to speak to a real person, you should be able to make them understand that when a vehicle is built it may not be registered for some time. It is for this precise reason that they allow vehicles registered after the Jan 1st 1960 cut off date for mot exemption to still be exempt as it is automatically presumed that they were manufactured before that date up until the 30th of January 1960, beyond that date they ask for verification.
It won't really matter whether they class it as either year as it won't affect the value, testing or anything else other than if you wanted to put a private plate on it that was a year too new.
But then as Rick has said, they don't know their arse from their elbow!
Having registered many American vehicles in the past they have always accepted the date on the title, I must admit sometimes I have had to accept an earlier year letter than it should be, I don't see their argument but it easy to get documented proof from the manufacturer and possibly the supplying dealer they can't argue with that.