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The idea of Jerry having a show in Japan isn't entirely far-fetched; his old college buddy even asks, "So, would have done it in Japan, but in English?", to which Jerry says he doesn't know. Japan actually does have a rather large English-speaking community, particularly Okinawa, so it wouldn't be entirely impossible for Jerry and George to do their in-universe show over in Japan.
In "The Finale", the officer keeping an eye on the gang in lockup says that the Good Samaritan Law they were arrested for breaking was based on a French law. The gang was on their way to Paris when their plane went down, so even if they had managed to get there the same thing probably would have happened to them. Karma's a bitch.
The sub-plot in "The Abstinence" of George becoming more intelligent by forgoing sex and Elaine becoming less intelligent for the same reason makes more sense when you remember the fifth season finale ("The Opposite"). There, the plot was that whenever George gained a success (got a girlfriend, got a new apartment, got a job), Elaine would suffer the opposite failure (broke up with her boyfriend, got evicted, lost her job) due to Jerry being "Even Steven".