Throughout Feud: Bette and Joan, the show intercut the main story with interviews from a documentary about Joan Crawford made in 1978 following her death. Those brief moments with old Hollywood stars Olivia de Havilland and Joan Blondell provided exposition and backstory that would have felt out of place in the main narrative but which were necessary to understand what was going on. In the finale, they were joined by characters who had more of a presence in the series, like Aldrich's assistant Pauline, Mamacita, and Victor Buono. These people had a lot of insight into Crawford's relationship with Bette Davis, but is the Joan Crawford documentary in Feud real? It could be, at least partially.
In 1978, an episode of the BBC documentary television series Hollywood Greats focused on Crawford, but none of the people featured in it were shown on Feud, and vice-versa. It's unclear whether inspiration was taken from this when crafting the documentary aspects of Feud, but it wouldn't be surprising if it was. The documentary in Feud appears to be wholly fictionalized. However, Hollywood Greats does address Crawford's dedication to both her career and her image, as well as her inability to let go of her facade in her daily life. Many of the people commenting on Crawford in Hollywood Greats had worked with her, and much of their insight on her wouldn't be out of place in Feud.
But Feud isn't just about Joan Crawford, and neither is the documentary footage that frames the series. It's about Crawford and Davis: how they impacted one another, how they mirrored one another, and how they acted as unwilling foils to one another throughout their long careers. Hollywood Greats doesn't spend much time at all on Davis or Baby Jane, instead exploring Crawford's youth, her early career, and her personal life.
For all its fictionalized moments, Feud still managed to remain mostly accurate to the true story it was trying to tell. While any dramatized version of real events will take some liberties, Feud was able to reflect a deeper truth about Crawford and Davis and the twin journeys they were on throughout their lives. At times the documentary aspects came off a little clunky or not entirely needed, but they gave context to what was going on onscreen.
While Feud could have taken inspiration from Hollywood Greats, it was simply telling a different story about Crawford.