CerinoDevoti: I can't see that^ as even a remote possibility because the US, Canada, Cuba and Mexico all have their own representation to the United Nations. Scotland, Wales, England and Northern Ireland are represented at the United Nations under the banner(flag) of the United Kingdom. I still think that's the reason WGT uses the flag they do for those Countries.
What about Jersey, Guernsey, Isle of Man? They do not belong to the UK, they have their own flags, but they are not in the UN by themselves - I'd guess that a British or Crown body will represent them.
I've been trying to get behind the reason of WGT flag or no flag but I didn't find the point until now.
Most mysterious is Antarctia which is not a country or political body of it's own - it's divided between several states. This makes it difficult to seek legislative or fiscal reasons for the selection.
To me it's clear (sorry, folks) that the parts of the UK have no
international standing of their own, just like the US states or the
German Länder. Therefore, it's my firm conviction that there will be no English, no Californian nor a
Bavarian flag here.
In my defense, I have a Saltire flag in my car window, and I proudly use two(!) pitch mark tools with the same sign. I love your countries!