What is the convention for Classic Music Names?

[Burning Petard]

Just listened to Mendelsohn concerto for two pianos in A Flat Major.
Perhaps best known classical piece is Beethoven's 9th; its conventional title is Symphony #9 in D Minor opus 125.

Why include the "key" it is written in for the title? Is there some other Beethoven 9th, but in the key of C Minor? Is that some hint as to how it is gonna sound? Did the patron paying for the composition specify just what key is was to be in? Can't any musician just look at the first page of the music and see the key signature indicated there in the first bar?

Enquiring Minds Want To Know.

snailgate, with really obscure trivia keeping him distracted.

[Scooter]

Titles in the classical period were used more to categorize than to describe, and the most common way chosen was by genre and key. Titles were not intended to be unique, although some composers would number their compositions of the same genre (Sonata No. 1, 2, 3, etc.). Pieces with similar names (Bach, for example, wrote four pieces called Prelude and Fugue in A-minor) were distinguished by the use of opus numbers, which were intended to number all pieces by the same composer chronologically, but did not always do so consistently.