You need to contact ATB Sales
http://www.atb-sales.co.uk/
I dont know how to get the date of manufacture but if you find out then let us know. The very early bikes did not have wheels on the racks and I think the front fork design was different. More recent models have a sort of double seat post clamp. I have also noticed that the Mezzo badge is different colours but I don't know if that is for the different models, mine is red/brown but most I have seen are blue.
Hope that helps, I am sure someone who knows more about than me will be able to give you a better idea.