If you add the two columns (including SORN'd cars therefore) you get the number known to the by the DVLA as still registered and existing in the UK and NI. At least that's the way I read it? That will include any UK registered LHD cars too of course.

Abroad for adding up the south-paws is almost impossible that way; they are too scattered, and not all local licensing authorities in different countries make similar data available.

David