Here's a thought:

The 1954 definition tells us nothing about how a song/ tune sounds, only rules about how it came to its current state.

Reggea, Ragga, Hip-Hop speedmetal etc attempt to describe how something does sound, not the process of how it got to sound like it does.

Therefore, I suggest that the 2nd group of labels is more useful than "Folk" if you care what music SOUNDS like rather than its provenance.

Can I go back to sleep now?

Cheers

Paul