Towards the end of The Rise of Skywalker, in the final confrontation scene between
Rey and Palpatine
Rey hears the voices of many previous Jedi. This question tells us that Alec Guinness is credited with one of the lines but he died in 2000, well before the character of Rey was developed.
If he'd said "Use the Force" or something similar, or the character had been part of the original trilogy (and so they'd had unused lines they could reuse) then I'd understand but short of some techno-jedi I'm confused.
How did Sir Alec Guinness have a credited speaking role in a film more than 19 years after his death?