Well, the idea here is showing how Dave remembering things convinces Oswin to try. That's the main connection missing, and that's precisely what makes it difficult to point out what it is. There are a number of options to how that could play. Maybe it was due to Florencia proving her point. Maybe it was just the sheer absurdity of the experiment working at all. Or it could also be something that Dave lets slip out when talking about the approaching events. How the vacation is going to be a bad idea, and realizing Roswell is in dire need of a course correction, possibly in the form of that medicine being made available to him. The other thing would be showing why calling the vacation off works this time, but my guess is that Dave's inherited memories effectively makes him a different person than he would have been at this point in such a way that the potential dangers never arises. These are the 2 selling points that explain why the true end works out. The medicine effectiveness isn't as important.
Still, I don't want to be nagging so much on these details. They don't detract at all from the rest of the story, which is really fun.