I think there is a lot of confusion cause in Jamaican music...the same thing can be call many different things!
When was the first time you heard the music been called "Dancehall"
This is my recollection....and corrections / amendments are very welcome.
From around 78/79 there used to be mentions of "dancehall style"...that was the so-called "rubadub" period....mostly recyclyng Studio One riddims with new lyrics relating to a "local" focus.
The Radics ( and Sly&Robbie) popularized the new type of arrangements.
A few years later that style was dominant and some albums were title "Ina dancehall Style".
What was the first album entitled like that? Sugar Minnott in 82 maybe?
But Dancehall as a coined word to refer to the type of music ( a sustantive not an adjetive) started around 87 IMO. The first time I heard it as name for the music it was by Lt. Stitchie on a Rodigan programme....I was a bit surprised that "Dancehall" was the name by jamaican artists for the current type of music. I used to call it Reggae and to me it was just a new style of Reggae (electronic / digital) and that was what the "experts" use to refer to in specialized magazines like Reggae Quarterly!
Rodigan, funny enough, used to call it "Ragga" (that was the name in the UK....exactly the same music). In other islands of the caribbean they called it "Dub" (nothing to do with Tubbys/Jammy/Scientist by the way).
I never read or heard anything that refer to the music itself as "Dancehall" before 87.
And I never hnheard in the early 80s anybody calling the current style as "rubadub" like a lot of people (in the USA and Europe ) does now.
Mind you, none of the millions of soldiers that fought in the First World War called it like that....the name was coined 20 years later!