See link below.

Model code 309 from 1971?

Get those smartphone translation apps out! 

Seller has some other interesting brochures.

Motorcycle Yamaha Trail RT 360 sale brochure | eBay

 

Well there ya go. I've been calling it wrong RT1 all these years. Down the page it says 1980 but anyway.

Interesting, I kindly received these images from enduronut - I was trying to place the 309 model.

These images are from July 71 JDM

Interesting both called RT360.

"Down the page it says 1980 but anyway."

Probably a typo.

yamayeeha - interesting that there appears to be more than one model of the RT360. Unless, of course, Yamaha's marketing team went off and did their own thing with model names on brochures (they did this with one of the UK RD models).

Having a number of JDM brochures .
The 360 was called RT 360 , which applied through piston port to reed valve motors .
The 250 was called DT 250 likewise , 175's were CT 175 , and 125's were AT 125's .
All marketing I guess , as various Japanese bikes ( and cars ) had different monikers ,
around the world , depending on market preferences .

I agree...  Yamaha did include displacement along with their model letter codes a lot in their literature...  I see including displacement after the letter code more as "marketing description" and not a true Yamaha model designation. 

Nobody but an enthusiast would know "RT" equated to a "360" displacement so it makes sense to include it.