I want to know the answer to the following question:
What have pieces published after 1857 been given rather than opus numbers?
All the background I'm provided with is that "The present standard musicological reference for Chopin's works is the Kobylańska Catalogue (usually represented by the initials 'KK'), named for its compiler, the Polish musicologist Krystyna Kobylańska.". Is that enough to answer the question?
Answer: no