Thanks for the link but this only covers the current standard. There are very numbers of vehicles on the road which have plates based on several previous standards as well as personalised 'cherished' plates which have all sorts of weird formatting.
If you search the comments for 'LLL' you'll find a separate thread which covers several of these.
Given that we're IT geeks here I should probably try to prove my point by writing a pseudo-code number plate parser which tries to validate all the possible variations. I think we'd conclude at the least that the task is complex and quite hard, but also that there's many scenarios where we just don't know for sure.