Here’s the thing: anything in public domain is usable. So if it was written before 1925, you can quote it in an epigraph or make a mash up using the world and characters (like Pride, Prejudice, and zombies).
If its not in public domain you have to get permission from the author or their estate which may involve paying a fee for use.
In terms of retellings or reimaginings, could you technically retellings or reimagine something recent? Eh, you could probably use something as a springboard to inspire you (a la 50 Shades of Gray) but it has to be all completely your own words and if it feels too similar to the original no one would buy it.
