Langford was nothing special in his craft from what’ve we’ve got horrendous film of. He didn’t have something you couldn’t see in better film quality in another fighter. if you wanna see that long out reaching guard and kinda oldie style in action just watch Saddler FFS.
I should have used the work unique. He was obviously one of the greatest of all time on paper but you can gather more valuable info watching other masters Langfords film and time period really makes him not that valuable for research and actual practice which is what I think the OP is looking for.
Langford was an early Louis. He spent his entire time in the ring, however long that lasted, trying to convince his opponents it was safe to punch at him. That was his job: make his opponent believe it was safe to hit him. These are the most deceptive and difficult fighters to unpick on film.
Oh, then it seems that I misunderstood you. I think I agree then, we don't have a lot of Langford footage (with questionable quality) and although he showed some nice tricks here and there, you can learn more from other fighters.