Maybe this little puzzle can be solved by a guitar genius with a ph.D in musical history.

I recently acquired a Sigma acoustic ("Sigma Guitars, Est. 1970") that came WITHOUT a Sigma label. Based on my own rudimentary skills, I'd say it's of Japanese manufacture. I've snapped some photos (spatula headstock, early tuners, plain, thin, line down the back of the guitar) that may be a tip-off. But the most interesting characteristics were the square, black and gold "Picador" label and what was below it. I peeled back the label and was expecting to see the common Sigma/C.F. Martin/Model stamp underneath, but there was only the number "2".

My questions: What model and year is this guitar? But more importantly, does anyone know for sure how Sigma/Martin treated what I believe is a second-quality guitar (it has a splotchy glue job inside)and where this guitar actually originated? I've read some interesting theories, but the information is pretty vague and mostly unsubstantiated. Thanks for any feedback you can offer!