You're quite right Jerry, I think TFL haven't been upfront about this, or that Euro 3 bikes registered prior to the date will be exempt.
This is the information from their website. It seems to state that the date is the only cut off, hence my email to them about the emissions standard of the actual vehicle (as it left the factory)
https://tfl.gov.uk/modes/driving/ult...e?intcmp=32646