yeah cart is sorta like lockpicking in that gains will stop at a certain point & then you can only gain from specific things. For LP its doing dungeon chests & such after 95.0, for cartography, at 99.5 you can't gain makin world maps anymore, you have to actually decode Tmaps, levels 2-4.
Of course, getting discorded as mentioned is the other option, but with GGS it shouldnt take too long by just decoding maps
GL