I've illustrated many different kinds of stories, but I've had great fun taking on some well-known fairy tales. The three I've done, Hansel and Gretel, Rumpelstiltskin, and Rapunzel, are all tales from the Brothers Grimm, although they have their own histories. There has been probably even more fun in learning about the stories than in illustrating them.
Stories are always in flux.
Wherever a story comes from, it was the property of living storytellers who, even while repeating stories they knew, would be influenced by other stories. They might add a detail, or weave together strands of this one and that one to make a story better, or to make a point. Which is just what a storyteller of today would do. I could have set the tale in any time or place, historical or wildly fantastical. So I felt that providing the reader with a sense of a solid, historical world would heighten the experience of seeing, for instance, a tower with 50 feet of red-gold hair hanging from it.