Well I think I completed the grid correctly, and now, like others, I'm having a lot of trouble solving the rest of the puzzle.
The name common to both expeditions *seemed* obvious, but that would result in code options six of one and five of another. Have I got the wrong name, then?
I also still don't understand "adding a line above the grid, to confirm A". Just making sure that H in the title with a single pen stroke scarcely "confirms A", does it?
Hugely enjoyable puzzle though and these final hair-tearings are just part of the fun... probably!