From Sathyanand’s Blog:
“The Greek poet Homer (probably) dictated the entire Iliad and Odyssey because, according to tradition, he was blind.” ~ says Michael M. from Daily Writing Tips.
Dame Agatha Christie dictated perhaps half of her 66 famous mystery novels. Science fiction writer Kevin J. Anderson says, “It’s been about fifteen years since I gave up the keyboard and took up a recorder for my first drafts.” He is the author of 56 bestsellers, with more than 23 million books in print worldwide.
Legendary writer Sidney Sheldon wrote all his 18 novels by dictating. “Each morning from 9 until noon, I had a secretary… I wrote each morning — or rather, dictated — and then I faced the TV business.” On the best days, he dictates close to 50 pages.
Link to the rest at Sathyanand’s Blog
Doesn’t matter if Homer was blind or not. He was pretty clearly operating in the tradition of oral-formulaic poetry, retelling the story to some degree every time, and always verbally.
What was written were transcriptions, and the (various) sources no doubt varied it themselves to some degree on each occasion.