Naming of classical pieces boils down to whether said pieces can be confused with any other.
Thus, FÃ¼r Elise is hardly ever written as "FÃ¼r Elise in A minor, WoO 59", because no-one else has ever composed a piano piece for Elise (except me, for a previous ex, but that's another story, and too sad to relate here
On the other hand, Chopin's E minor concerto benefits from its key being given, because it was the second to be composed, yet it's known as Piano Concerto No.1, Op.11, whereas its predecessor is No.2 in F minor, Op.21 - because the earlier No.2 was the second to be published.
Ditto for Beethoven's first and second piano concertos. No.1 in C major was composed after
No.2 in B flat major. So, best to give the keys, as nobody remembers the opus numbers. Anyone who knows those concertos can easily discern that No.2 is the more juvenile of the two.
Then, there are works which are not really in a specific key, though they might superficially seem so, like Berg's sonata, no nobody identifies it as "Sonata in B minor", unlike for Liszt (or Chopin). And then there are works that starts in one key but finishes in another, like many of Mahler's symphonies. So, we just name them Symphony No.x
, where x is a number between one and nine (inclusive), as Gustav didn't give opus numbers to his music. On the other hand, his Das Lied von der Erde
is a symphony in all but name, but his superstition (common to all great people
) forbade him from calling it No.9 - with good reason, because he didn't live to complete No.10. The moral? Don't compose your ninth symphony until you're ready to depart......
Scriabin starts his piano sonata cycle with key-centred pieces but then gradually abandons tonality from No.5 onwards, so we don't name them by their keys. But though we use numbers for identification, his last sonata was No.10, yet he composed twelve sonatas........