The word Marijuana (or Marihuana) was the Mexican word for cannabis. I say Mexican because I don’t know if it is from Spanish or one of the indigenous languages, but it is what the Mexicans in the Southwest called it. Reefer would have only been common in Jazz communities, i.e. inner city black. I don’t recall seeing when grass or weed came into use, I would guess in the 60s.
The bottom line is that Mr. and Mrs. average American would only know it as hemp or cannabis. They would have known cannabis as medicine and hemp as what their clothes and paper were made of. Given the economic situation at the time even if more people knew that Marijuana and cannabis are the same, I doubt it would have been enough to overcome the perfect storm of Cronyism, racism and political expediency.