One particular item from ENT3 has confused people. The Xindi's Guardians, despite their monkeying-about with the timeline, seemed to provide none of the components for the Xindi weapons, which were largely engineered by Degra. However, it's suggested that some of the components for the prototype that struck Florida were from the future, as deduced via quantum dating.
While it's possible that the early prototypes were supported by Sphere Builder components (they were, after all, able to leave a guy as a guinea pig in "Harbinger", not to mention building the spheres, so it isn't like they couldn't drop stuff off), there is another possibility.
As seen in "Little Green Men"[DS9], kemacite has temporal properties when exposed to high energy, and is also a material highly regulated by the Federation. It's generally assumed, though not proved, that this material is the same as kemocite.
However, if it were, it could imply that the Xindi prototype weapon actually had no components provided by Sphere Builders, but that the kemocite in the weapon just happened to impart a temporal signature on some of the components. These components would thus be made to appear to be from the future.
Thus, the cornerstone of Archer's argument that he needed to go into the Expanse would've been based on coincidence, not fact.
(Also, given that it was Future Guy who tried to give him the heads up, one is left to ponder the possible manipulation.)