If anyone says BOS or Enclave I'm going to have to say no to it directly.
First let's take Enclave, they're a military organization who has very strict policies with it's soldiers, scientists and officers.
If anyone used Jet they'd likely be punished harshly and the Jet showed up before them in CW anyway.
Now the BOS, I don't think it's feasible here either.
Consider that the BOS came from the west across an entire continent, and it's not like they walked non-stop, they stopped at places to loot and kill stuff too.
So, why would they bring with them Jet? Why would the elders back west approve of it? Why would Lyons approve of it?
They wouldn't.
Why couldn't a few BOS members have been addicted and brought them with them?
What? They had a huge stash of Jet to use all the way over to WC?
Like Lyons and others wouldn't notice if their soldiers had a huge stash of inappropriate chems with them.
Or that the supply wouldn't run out.
Why couldn't someone in Lyons Brotherhood have made Jet in small doses for him/herself?
Again, I don't find it feasible to think that no one else noticed it and that (s)he is hopped up on Jet not to mention producing it.
Remember that they have to travel a long way, which means that (s)he wouldn't have all the time in the world to produce Jet either.
So they would notice the withdrawal symptoms that appear after not being able to produce any Jet for a while.
I don't see any way that the BOS or Enclave would bring it along with them.
So how did it came to be in the east coast?
Trading?
Uh-huh, I'm sure that traders went through Legion lands with illegal chems from the west just so they could sell it in DC.
Now, what logical reason would there be for Jet, a chem created in 2241 in Reno, to be in the East Coast considering that raider-utopia Arizona or Legion was in the way?