Need some help clarifying this please.

I especially want to know:
- What year was the extra brace on the chain stays behind the BB introduced?
- What year was the extra brace plate behind the seat post clamp area introduced?

Photos and references would be good.

the "seatclamp" gusset was found approx mid-ish 1982 til mid-ish 1984. japanese made.

Awesome question, I have a Redline PL-20 that has that triangle gusset behind the seatclamp area. All the digging I did brought me to it being a 83 which puts me right at what you said Mr. coasterbrake. However I didn't know it was Japanese made .

Mark