Where on screen is it stated the 2245 launch date?
Enterprise is not titled Star Trek... all Canon references are to Star Trek, Star Trek: TMP, Star Trek II: TWOK, Star Trek III: TSFS, Star Trek IV: TVH, Star Trek V: TFF, Star Trek VI: TUC, Star Trek: TNG, Star Trek: Generations, Star Trek: First Contact, Star Trek: Deep Space 9, Star Trek: Voyager, Star Trek: Insurrection, Star Trek: Nemisis.
notice the patttern for the Star Trek series listed...
now what makes this different than Enterprise?
Enterprise is not titled Star Trek : Enterprise.. thus it is not Star Trek.. it is listed as "Based on Star Trek created by Gene Roddenberry".. as such, an extrapolation of a possible pre history.. since Star Trek is not a direct title name, the series Enterprise can be dismissed easily...
Also, if you go back to Gene Roddenberry and / or his wife, Majel Barret.. Gene stated that canon is what is shown on screen and what is FIRST SHOWN onscreen is establised canon,, anything after the establised canon is someone who can not do their research and should be disreguarded...
Also, B & B stated that they were going to do their best to change Trek into thier image and completely wipe out the Trek of Gene's dream, which is why Majel Barret refuses to have anything to do with Enterprise and Paramount refused to allow the series to be titled "Star Trek: Enterprise".. as such, Enterprise, since it is not titled Star Trek, and because it violates previous established canon, and because Majel, Gene's widowess, spits on the series.. it again can be easily dismissed...
but I'll not argue that point again..
Canon is establised in Trek as when first aired on TV... since TOS was first aired, the NCC-1701 is Starship Class, the NCC-1701 Refit is Enterprise Class, the NCC-1701-A is Constitution Class, the NCC-1701-B is Excelcior Class, the NCC-1701-C is Ambassador class, the NCC-1701-D is Galaxy Class, the NCC-1701-E is Soverign class.. as canonized by order of first airing and in accordance with Gene Roddenberry's dictation of how Trek canon is established... Anything else is pure fandom and conjectural.