The Starfleet in Enterprise isn't the same Starfleet as the rest of Trek?
When GE Fabbri's "The Star Trek Fact Files" began incorporating episodes and tech from ENT, they added a new cardboard divider for "Earth Starfleet", since the material and dating for the founding of the UFP and Starfleet was already established as a much later date.
Was it established on TV/film or just in the manuals? I can see why the later Fact Files would have to fudge in order to fit the new issues in with the old, but unless it's canon surely the new info (i.e. Starfleet in 2151) takes precedence. TOS made many "Earth Command"-type references, too.
That said, ENT retconned and ignored all sorts, so I don't think it matters any more than Picard's comments about "disasterous" first contact with the Klingons, Worf's "there were no phasers in the 22nd century" and Spock's lecture on Romulan War-era technology and everyone's amazement at a cloaking device.