It's not that straightforward. The way the European regs are drafted, they nearly always have a phased implementation period. There will typically be a date from which "new types" of van need to comply, and a later date from which "existing types" need to comply. Even at the end of the second date, there are bound to be loads of vehicles that were manufactured before the deadline, sitting in fields waiting to be sold and registered. There is therefore an "end-of-series" derogation procedure whereby a manufacturer can register (say) Euro 4 vehicles even after the deadline has passed, PROVIDED they were built before the deadline. There is more than one way of working out how many vehicles can be derogated, some use up to 30% of the previous year's production, other's use all the production from the three months leading up to the deadline, etc. So basically, the only sure way would be to phone the manufacturer with the 17 digit VIN code of the vehicle and ask them what emissions level it was made to. Very recent ones might even have it on the registration document.