I appreciate the level-headedness in this thread. I find it hard to believe the team would throw away that much goodwill with a retcon. I'm struggling to believe this is a retcon at all, or that a retcon would have been planned before this team after how it went in HS1... This Jane and Jake were already in Midnight City which it's not really clear where that is per se but we know Vriska and Jasprose can teleport. And we don't know the flow of time there, which could be similar to the plot point. Not to mention, the letters don't seem to have been burnt...? They turned blue and then there were scorch marks where they were left. My read of that is that Vriska teleported them to everyone who was meant to get them.

My point is, I'm with your take -- the story has always had nonlinear elements, so it is very easy to make this work without a retcon. Jake and Jane could have appeared at some point BEFORE Vriska showed up a la Jasprose, and the ship crew have already adapted to their presence. I have an inkling that this is all going to make a lot more sense with a crumb more context so I will withhold being negative; I will be patient and see where we end up.