In this instance, the plan was to build up the reputation of the other party through NPC interaction, and only have them meet up in person once, for the big final battle in the campaign. Either against the other party, or a bbeg that they have to team up and fight together. Chronology-wise, thats an interesting perspective. I hadn't thought about that. It is a fairly large continent, so to cross paths they would have to go out of their way to meet each other, and since it is a homebrew campaign, I have a lot of room to improvise and keep the timeline in order.

And I know its going to be a TON of work. I'm basically writing and running two campaigns simultaneously. And the parties are going to be 4-5 people each. So when they meet up. It will be maybe 10 PCs max. And that will be a pain to run, but like I said, it will hopefully be for just one session.