I have never paid as much attention to detail as you guys when watching the movies. So i never really thought about who trained obi wan. i just assumed after qui gonn died, yoda finished his training. as protocol droid said, its safe to assume certain things happened even though we didnt see them onscreen. time did pass between the PT and the OT (i dont recall how much since, again, im not good about the details). during that time, obi wan clearly could have finished his training with yoda, as they both allude to in their OT dialogue.

As for yoda as a hermit, i think PD explained that very well and i dont need to revisit that. but i do find the point raised by darklordoftech to be very curious. Is it actually the case that the rebellion doesnt know who yoda is, or is it just that he has been hidden away for so long he isnt given much consideration or thought by them? is it possible they think he is dead?