Uk Plates (Copied info from the site):
As usual, using "Vehicle Enquiry" from www.vehiclelicence.gov.uk/EvlPortalApp/index.jsp
It is also possible to guess an approximate year from first or last letter, but I do not know how.

These pages help with the identification of the years:
www.ukcar.com/features/reg_year.htm
www.dvla.gov.uk/vehicles/regmarks/reg_marks_memorytags.htm

You can tell what generation a plate is from (example: "The Russian" Alaska license plate is used from 2001 to date, and the blue-on-yellow Alaskan plates were used from around 1985 to 2000, my Tempo has a yellow AK plate.

The decals on US plates generally refer to the current year and are generally tax related. In the past new plates were issued for each car every year with the appropriate date but over the past 20 years or so the plates were not reissued but a new current date decal is provided to indicate current registration and tax paid.

In general, US plates do not have any information (that is redily available to the public) that can be used to identify either the make, model or year of the car.

For Sweden just visit https://www21.vv.se/fordonsfraga/ and enter the license number in the box. You get brand and model (Fabrikat), year (Årsmodell) as well as a lot more info like number of owners (Antal ägare).

Ya I know, but it seems like a good idea if you have like 7 stickers all over your plate to trip up the police.

As far as I know as long as the sticker is visible and legible, it's legit. I've seen a few cars where people ran out of space on their old plate and started putting it on the other corners.

Some people just stick the registration number anywhere (maybe to confuse the cops). The previous owner of my Tempo did that on the rear plate.

If you want info on cars with a license from the Netherlands, you can use this link: http://info.apk.nl/ovi/OviInvoer.aspx

It will provide some technical details about the car, aswell as the date it was first registered in The Netherlands.

If the search doesn't return a page with data, the car isn't registred anymore, so it eaither scrapped or exported.

We use a month in a large digit in the middle of the sticker with the year vertically on one side. The color changes every year.

This is a pretty cool site with all the different state's plates from the last couple of decades:
http://www.plateshack.com/platelist.html

But the year on the sticker stays the same, right? And is there a different colour for each. Because the numbers are pretty hard to read, in Britain it's easy because we had a different letter prefix for each year, now we a new numbering system. And on the Maserati, the 3 does mean 2003, right?

I've also seen a lot of plates with squares to put the stickers in but no year sticker.