Beethoven wrote nine symphonies; Brahms, four; Sibelius, seven; Shostakovich, fifteen. Those numbers aren’t likely to change—only the fringe types suspect there might be a Beethoven Tenth still floating somewhere in the void, or that Sibelius didn’t really burn up the manuscript of the incomplete Eighth.
Even Haydn’s symphonic output has steadied: I haven’t come across any claims that there might be other than 107 symphonies total, numbered up to 108 due to a scholarly misplacement of one work. No: the last-written Haydn symphony was No. 104 in D Major, the "London", while 105 refers to the marvelous "Sinfonia concertante" of the London period, with 107 & 108 taking the place of the symphonies formerly known as ‘A’ and ‘B’.
But Mozart? Now there’s a disgraceful mess for you. I wonder if anybody will ever tidy it up for good. One look through Appendix B of Neal Zaslaw’s Mozart’s Symphonies bears appropriately eyestraining witness to the situation, not only in regards to the symphonies the fellow actually wrote, but as to our identification of them as well.
Breitkopf & Härtel’s numbering system, despite its many flaws, has tended to hold sway with the Mozart symphonies. After all, Mozart Symphony 40 works quite well for everyday conversation; it’s the "big" G Minor, and we can refer to it as either 40 or the G Minor and folks will generally follow along. One could be oh-so cerebral about it all and refer to K. 550, but a blank stare is the likely outcome. Ditto Symphony 41, a.k.a. the "Jupiter"—does anybody save your basic pompous windbag ever call it K. 551? (And don’t get me started on twits who insist on saying "KV" instead of "K".)
Back in those halcyon days when we still had elementary-school music classes, there was only one correct answer to the following test question: "How many symphonies did Mozart compose?" Anything other than "41" would land you in Miss Thistlebottom’s iron-spiked doghouse. I grew up with a big "41" branded into the surface of my frontal cortex. But a glance through the Breitkopf & Härtel numberings—often used in complete sets of the Mozart symphonies—reveals that the numbers go marching up, up, and beyond that supposedly terminal 41, all the way to an eye-popping 55.
O Miss Thistlebottom, how could you? We trusted you, we believed in you, we were scared shitless of you, and just look what you did. O Miss Thistlebottom, if Wolfgang Mozart composed only 41 symphonies then I’m King Ladislaw of Spritzbergen-Mädchenstein-auf-Danau.
Maybe the old girl just couldn’t face the grisly reality, because once you hit those trans-41 symphonies all sense of order goes out the window. The Köchel numbers—which are organized chronologically—go haywire. By way of example, observe the relationship of Breitkopf & Härtel numbers to Köchel for the later symphonies:
No. 35 "Haffner" K. 385
No. 36 "Linz" K. 425
No. 38 "Prague" K. 504
No. 39 K. 543
No. 40 K. 550
No. 41 "Jupiter" K. 551
Such a fine, orderly state of affairs, except for the absence of Symphony No. 37, which has been determined to be the work of another composer. Each symphony follows the next in a tidy order, No. 41 being written later in Mozart’s life than No. 35. How lovely.
Now let’s cross the Rubicon to the trans-Jovians:
No. 42 K. 75
No. 43 K. 42a (formerly K. 76)
No. 44 K. 73l (formerly K. 81)
No. 45 K. 73n (formerly K. 95)
No. 46 K. 111b (formerly K. 96)
No. 47 K. 73m (formerly K. 97)
No. 48 Anh. C 11.04 (formerly K. 98)
[No. 49 banished]
No. 50 K. 141a (formerly K. 163, formerly K. 161)
No. 51 K. 196 (formerly K. 121, the overture to "La Finta Giardiniera")
No. 52 K. 213c (a mix of K. 208 and K. 102, the overture to "Il Re Pastore")
[No. 53 banished]
No. 54 Anh. C 11.03 (formerly K. 74g)
No. 55 K. 45b (formerly K. App. 214)
Oy, what a mess. The lowest Köchel number is the highest B&H number, ferkrissake.
Obviously the scholarly community has been up to the wazoo in second thoughts, given those "former" Köchel numbers that reflect earlier editions of the catalog. In all fairness I should point out that shifting Köchel numbers are by no means restricted to the trans-Jovians. Consider Symphony No. 27 in G major, indisputably Mozart’s work, currently dated 1773. However, the poor thing has been slapped around unmercifully, starting out as K. 199, then receiving the less dignified K. 162a, finally degraded to the distinctly second-banana K. 161b. Zaslaw points out that the date on the manuscript is "defaced and difficult to decipher with confidence; the paper is a type used by Mozart between about March 1773 and May 1775", several chronological readjustments being the result.
Just to ensure thoroughgoing confusion, a few more works that are almost certainly not by Wolfgang Mozart pop up in catalogs—the "Neue Lambacher" symphony in G Major (Leopold Mozart) and some assorted bits and pieces.
I’m still in favor of identifying the Mozart symphonies by their B&H number, but I must admit to feeling uneasy about the trans-Jovian group, after Miss Thistlebottom’s thorough brainwashing. Somewhere deep inside my subconscious I can hear her outraged shriek: What’s this NONSENSE about Mozart Symphony No. 50, you stupid stupid STUPID boy?? How many symphonies did W. A. Mozart compose? How many? [Whack] HOW MANY???? [Whack Whack]
But there might be a practical way to deal with both the mess and my childhood trauma. My friend and colleague Conrad Susa once opined that Mozart was a "late-blooming" composer. That’s vintage Susa—quirky, seemingly nonsensical on the surface, but sound as a nut when you think about it. Conrad was pointing out that Mozart didn’t really blossom into Mozart until the final third of his life—that decade of the 1780s through his death in 1791. I think most of us have discovered that earlier Mozart tends to run towards decorative, unremarkable Rococo stuff, although wonderful flashes of the Mozart-to-come do brighten things up here and there. But anything with a K number earlier than 100 is going to be the work of a Salzburg crevette, of interest only to hardcore Mozart completists.
Thus my solution, seditious though it may be: O Miss Thistlebottom, you were right. I will stop with Symphony No. 41.