Finally, the possibility of Jupiter Lighthouse freezing Weyard is foreshadowed all the way back in VAULT after you exit the Lamakan Desert. If you talk to (or maybe mind read?) one NPC, I think either a man near the shops in the upper right or a woman near the inn (it's been a while), you'll learn that winter is coming sooner than anticipated and notably colder than ever before. Keep in mind this is well after you lighted Mercury Lighthouse.

Anotber thing, on the way to Kibombo a lot of NPCs in Naribwe have dialogue and thoughts that will mention Isaac's group. On the way back, NPCs in Naribwe and Madra will have different, additional dialogue and thoughts. They mention not only Isaac, but one person in Naribwe will mention a man named Agatio likely well before you meet him in Champa, so possible a first-time player probably wouldn't but could learn about him that way.

The most recent time I finished a playthrough of TBS+TLA, I made it a goal to talk to and mind read each NPC for every piece of dialogue. Did you know Susa has different dialogue and thoughts when you leave Gaia Rock before and after you trigger him telling you that he's on the ground because he's exhausted, not dead?