I am more knowledgeable but not qualified.
Copyright is quite complicated because there can be lots of different rights in a single item. For example, in a copy of Cinderella on the shelf in Waterstone's there can be copyright in the precise story, and then in the particular translation of that version of the story, and in the precise edition of that translation, not to mention in the illustrations, cover art, and so on.
Translations are considered derivative works (see also condensed versions, musical arrangements, screenplays, etc) but the author of the translation does have rights to the derivative work itself. Translations and editions are typically commissioned or at the very least authorised/licensed by the copyright owner.
It's a peculiarity of intellectual property law that you can legitimately own a thing whilst also infringing someone else's rights. Imagine a big field with a house built right in the middle. The big field is the original story and the house is the derivative work. Unless the owner of the big field grants certain rights to the house owner, there ain't a great deal the house owner can legally do with the house.
You will recall that Fifty Shades began life as Twilight fan fic. You will note also that there are pretty much zero characters or scenes from the latter in the former: that's deliberate. It's very much "inspired by the feel of" rather than "derived from". Fan fiction is quite a complicated area for copyright issues not least because copyright is geographical/jurisdictional and the internet struggles with that concept.
There are lots and lots of published Harry Potter sequels in China, for example, because they pretty much DGAF about Rowling's moral rights or about copyright.
In the case of Cinderella, then, nobody could claim to be the originator of the general story - similar would apply to the Bible, Aesop's Fables, the Canterbury Tales and so on. But there will be extant copyright holders of particular editions of those works.
So if you write a lovely version of Cinderella, and do some lovely drawings, and convince Usborne to publish it, the copyright is new.
But if you write a lovely version of Cinderella in which there are singing mice, Disney will shout at you very loudly through their lawyers, because it would be a derivative of their version of Cinderella rather than the story in common use.
If you dug your great-great-granny's diaries from the 1890s, tidied them up and published them, you'd own the copyright. You could sell it to someone, or leave it to your niece in your will.
The date matters because copyright isn't an eternal right (unlike trade mark rights which theoretically can last forever) and they expire. You can revive your rights by issuing a new version, though. You can't infringe your own copyright, so if you make a minor edit and publish that, the copyright in the new edition would have a new start date. This is part of the IP concept of "evergreening".
(It's more complicated than that, but just to give you a flavour)
