I know Van Buren will never be seen as canon, officially, but there are so many things found in FONV and FO3 that were developed from Van Buren and it's prologue. Even some of the main themes you find in 3, I think, come directly from this prologue and is why some people who aren't familiar with it don't see it as a proper sequel to Fallout 2. If that's your opinion, I'm not going to argue and i respect that. According to VB prologue, with tensions growing between the NCR and BOS, Jeremy Maxson(leader of the BOS at the time) decided to expand eastward. He learned of the Peterson Bunker( a prewar personal vault for a senator and his family built by the Enclave, with Poseidon network communication and a library.) Jeremy sent the BOS to find the bunker, which is in southern Colorado, develop good relations with locals and guard the facility until BOS futher notice. So they found the Bunker and the group responsible was promoted. So if you find a bunker like this, belonging to a former senator, with tons of government inforamtion and communications...maybe Bethesda added to this "BOS expanding eastward" to DC. The bunker could have had info on Liberty Prime and Vault 87 experiments. I'm just simply saying Bethesda could have expanded on this idea, just never really explained it too well. Anyway..other places you might not have known the BOS are located are Montana(according to Elder Lyons) and Colorado(? Peterson Bunker, according to Caesar.)

Everyone knows Harold from FO1 and FO2 and it's in 2 we see the small tree appear growing from his head. In VB, Harold suffers the same fate he does in FO3, he becomes a tree, even starts producing fruit called "Sowat." Ever wonder why he has a tree growing from his head. To make it short, he was raised in Vault 29 as a child, left and found the Nursery, a plant and seed repository found in VB. He lived there for some time and when he left promised himself never to speak of the place so no harm would come to it. I believe he would visit the Nursery from time to time on his travels and if he had seeds on him when he was "dipped" in the FEV, just makes sense he might have a tree growing out of his head.

The New Plague was to play a major part in VB and we see mention of it in Point Lookout in Fallout 3 and why you find Chinese Stealth Armor at Hoover Dam in FONV...and i wouldn't be surprised if we don't see it again in FO4.

No, Van Buren has never been known to be canon but the events in its prologue have to be and that's why we have the New Plague, the Legion's dogs come from Denver, the NCR-BOS war, Circle Junction, COS, Caesar capturing BOS in Colorado and the fact the BOS are also located in Mojave and Montana,.. Fort Abandon, the Ciphers, the fact there isn't one in game reference to SF, and the list goes on and on.

I just find it very odd that every location in the core region is mentioned in FONV except for San Francisco. According to VB's prologue, it was destroyed by the Enclave after the destruction of the RIg. Many think that SF still must exist because there are so many oriental NPCs in the game. But according to VB's prologue, the NCR and the Shi set up a student exchange program and that is why there is Xian at Boulder Dome, a scientist there. They would have survived if SF was destroyed.