Between 5 and 6 the story about how they tracked down Han would be cool. But probably not a film they'd make.
This time line is confusing.
At the end of 5, Lando and Chewy fly off ahead of Leia and Luke to rescue Han.
At the beginning of 6, we see the rescue.
And yet according to the time line, a full year had past between 5 and 6 so I don't know what Lando and Chewy did for a year. Did any of the books talk about this period?
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and this is just my opinion but I don't want to see new actors play those roles in that time period.
I have no problem seeing a young Han and young Lando in a back story about Han since we did not see them in that time period in any of the movies, but we are very familiar with all the characters between 5 and 6 and I don't think I would like to see new actors in that time period playing the same characters.