Or they could just... you know, call Jet "meth?" Isn't that what Jet basically is? I mean, even if they don't want to call it that because of wanting to avoid that for whatever reason, they could still have it in a different form. Make it a powder or something. It's not like it's not obviously a drug in the first place.
Probably. There was a thing in the news before Fallout 3 about Bethesda renaming all the drugs in the game so Australia wouldn't ban it- they originally had 'morphine' that was renamed Med-X. Jet may have been meth, or something similar and renamed.
Personally, it doesn't bother me anymore. It
did bug me in Fallout 3, but I've come to just handwave it aside:
Myron is such a dick, I figure he probably had came across some knowledge of the pre-war Jet and then realized he could create a similiar, but more addictive, drug using brahmin dung and fungus. He's so arrogant and condescending, naming his new drug after the one that inspired it doesn't seem out of character for him.
He passes the new drug off as entirely his own thing, and anyone that finds an authentic, pre-war, "Jet" assumes it's Myron's- even if it's an entirely different drug.
With that (personal) retcon, the Jet on the East coast and the Jet Myron invented in Fallout 2 can both happily co-exist.