I imagine there are countless of individuals that are very famous within some region, but little known outside of it. It's not easy to have global recognition.

Yes, and it is also something that we are coming to terms with now that we have a more global community.

The hit in question, the one that outsold any individual Beatles single was from 1976. That was a time when most people received news from around the globe in print, with most of those print publications being regional and a handful being national. Something similar could be said for radio, though some people could hear stories from afar on the shortwave bands. That was more the exception than the rule though, typically of greatest interest to those who wanted to hear voices from their homeland or those keenly interested in learning about the world. (Even then, language was typically a barrier. When it wasn't a barrier, most of the stations were propaganda machines.)

Even though your claim undoubtedly remains true, at least we live in a world where those stories can leak out.

Rihanna sold more records in the UK than the Beatles. https://en.wikipedia.org/wiki/List_of_best-selling_music_art...

Although slavery is a society illness, the mixture of African and American (Caribean, South America, North America) cultures generated a huge musical heritage. Could this be the largest branch of music in history?