The first 3 letters come from abbreviation of lavatory, which I think in America is the can, john, whatever...
As to 23/25, my guess is the initials of a geographically significant point, though I could still be entirely on the wrong track since I haven't tied up quite a few things yet. On row 2, I can make the name of a person common to two different expeditions to reach the above point, using a couple of letter replacements.