There were lightsaber training scenes to be shot, but they weren't. My belief has always been that Luke was just left to trust in the Force to guide him as he fought. That's how it works anyway, seeing things before they happen and reacting quickly. Keep in mind Luke also ran off to fight before his training was done, so maybe it was still forthcoming.
I have to dispute the six months thing also. It's been said somewhere official (can't remember where) that these films cover one month, maximum. Luke got a super crash course in Jedi training, and had to rely on his raw abilities to last against Vader as long as he did. Vader wasn't trying as hard as he could, but whatever. Luke's real growth as a Jedi was in the six months between ESB and ROTJ, a time during which he built his own lightsaber and meditated and whatnot. There's a clear increase in Force proficiency between the two films, and building your own lightsaber is supposed to be a rite of passage to become a full Knight.