The current British registration system will show you the date on which the vehicle was first registered - in whatever country that may be. We bought our vehicles in April 2010, and that's that date of their "first registration", so they have plates showing 10, rather than the date we brought them into the UK or registered them which would have been 11.
If you're dealing with a vehicle which has a registration before the current system (back to the days of letters as prefixes) I'm not certain what the deal was. I seem to recall that when I brought my car in as a young Squaddie returning from a tour in Cyprus, the number plate I received was for the current year in the UK, but that recollection may well be inaccurate due to the large amount of Cyprus Brandy which was still in my blood stream at the time.
One other thing to mention is that the US manufacturers released their "2012 models" in about August or September 2011 - yeah, go figure. So that's an area where confusion abounds easily.
Also, the date of manufacture of the chassis may not be the same as the date of manufacture of the RV. When we registered our Winnebago in the US, we had to send the documents back to be re-done, because the clerk in the Department of Motor Vehicles had taken the date of manufacture of the Ford chassis (which was 2009) rather than the date of manufacture of the motorhome which was 2010. Having two pieces of paper with different dates on them must have been too much for them to deal with.
Hope that helps,
Jay & Elle
There are two excellent theories for arguing with women. Neither one works!