https://screenrant.com/star-wars-lando-clone-plan-boba-fett-ruined/
Early plans for The Empire Strikes Back would have made Lando a veteran Clone Trooper, which would affect the villainous and stoic Boba Fett.
Before Attack of the Clones showed us millions of clones who were all copies of the same person, I think there was this vague idea that the Clone Wars had clones from different original sources, not all from one man like how it turned out. If Lando had been presented as a clone in ESB, I wonder if AOTC would have brought back Billy Dee Williams and made Jango and all the clones look like Lando, or if they would have gone with the idea of multiple clone donors, since CGI de-aging was still a few years away (I think X-Men: The Last Stand was the first movie that did it).
And of course, during the time when the original movies were made, it had not yet been decided that Boba Fett was a clone.