Frederic Chopin
Works published since 1857 have received alternative catalogue designations instead of opus numbers. The present standard musicological reference for Chopin's works is the Kobylanska Catalogue (usually represented by the initials 'KK'), named for its compiler, the Polish musicologist Krystyna Kobylanska.
What have pieces published after 1857 been given rather than opus numbers?
alternative catalogue designations
Works published since 1857 have received alternative catalogue designations instead of opus numbers.
opus numbers