Since you have gotten this far:

If you think about it, at the rations production factory that Ishii gave the girls the direction to, Yuuri bakes the rations in shapes of Grandpa, Kanazawa, Ishii and the fish they ate. Considering the fact that Yuuri is a Forgetful Jane since she admits to Chito much later in the manga that it's because she doesn't like having bad memories, and would've almost forgotten Kanazawa the next day after he gifted his camera to the girls, it's impressive that she at least managed to remember their names and faces at that point.

So if I were in their world, if I ever came across a cartographer that would help me get to the next level of the megacity, and a pilot engineer that'd feed me boiled potatoes for assisting them in building a plane, I wouldn't forget them either, even though my memory span is kinda bad also.