So, as I understand the rules, you have your Phase 3 story, and then for the Phase 4 story, someone else jumps on your Phase 3 and adds their character to it. Then for Phase 5, someone else jumps on to someone's Phase 4 and adds to that, so everyone's Phase 5 should have 3 story parts, yeah?
How would you handle this if, say, you had another player join in two months down the line? Would his character's Phase 4 still piggyback off someone's Phase 3, or would you use some more recent story threads that came up in the sessions? Personally, it seems kind of silly to say "Yeah, you totally knew all these guys way back when, but you just haven't been with the party the last couple months for some reason and nobody's mentioned you." Sure, you could work that in, but that's dependent on the character and the campaign. So do you guys have your ways of handling this?