Everything you've quoted there has come back as matching mate, only discrepancy is chassis number which isn't there. The seller only had the defender for a few months, but claims he bought it in wales and drove it so England to sell for a quick profit. Through a bit of research, it looks like he does this with other vehicles.How long had the previous owner had the tratter?
Does the mot history for the registration match the vehicle?
mileage?
colour?
https://www.gov.uk/check-mot-history
Use the vin to find original spec details:
https://www.vindecoderz.com/EN/check-lookup
Have yer searched on the web for the registration on the vehicle plates and windows, and vin number/registration marked on the v5 log book, to see what comes up?
registration "aa33 gkn" is different to aa33gkn when searching, as the space makes a difference sometimes
If it is stolen or you think it may be stolen then you need to contact the police. On a technicality you would be handling stolen goods, if it were stolen, as you are in possession of the vehicle (you bought it and have it currently). At the point/time of sale the seller would also be in trouble for handling/selling stolen goods, if it were reported stolen at that time. If you choose to go to the police yourself it will hurt less than them pulling you over, or seeing it outside yer house and choosing to do a spot check.
If you contact the seller or anyone else that may be involved in it's theft... make sure yer tratter is hidden/protected. It (the evidence) may suddenly disappear if they're worried.
May also be worth mentioning I have a folder full of receipts/invoices/MOTs for the truck matching its reg/info dating back to the early 2000's