Lets get this clarified-- Firstly the term Rhumba-- is a catch all term.
everything commenced with " son ", and from that came Danzon.
This was the forerunner of triple mambo, Cha, salsa , guaracha and the extension of that construction ( the open box ) patterned after Bolero , which was adapted by Pierre into todays Intern. style of Rhumba .
The latin rhythms are far more complex, than just saying -- fwd , back or side .
The majority of social latin dances , bear little or no resemblance to the authentic form ( having researched and danced all style since 1940 with sq.rhumba,) thru todays versions .
Being intern. styled trained, it took many yrs of immersion into the latino community, to really understand the true essence of the many layered rhythms .
ALL latin forms , are based on the " call and response " theory .
And there are not 3 types of rhumba, but at least 6 . Socially, most only get exposed to 2 / 3 .
Freds patterned their beginning from danzon ( the true form ) A/ M opted for a system , that would incorporate the basic for teaching 4 different dances-- it was, and is , a sales tool .
Have worked for over forty yrs , for both organisations, and for the average person, the beginning is of no consequence .
These types of discussions, are for the purists , and only serve to enlighten newcomers to the many pitfalls that await in the social scene.
Lastly-- most latinos (which is most of my friends ) cannot understand what, and or why, the non latino community, has done to their heritage !!