Mozart, WA (1756-1791) - Symphonies w/ Mackerras & the Prague Cham Orch on Telarc - released as a 10-CD box at a fabulous price - just arrived the other day and starting my listening experience; I had 3 previous CDs of these works, but this is my first 'complete' set of the Mozart Symphonies; do own a number of different conductors in the latter half of Mozart's output in this repertoire - in fact, love this guy in a variety of different approaches.
So, my reason for posting is not to start a discussion of Mozart 'Symphony Sets' (we already have these threads), but to discuss several issues of Mozart's output in this genre: 1) Authenticity, esp. of the early Symphonies, e.g. on the first disc of this set the No. 1 Symphony, likely authentic, was composed by Wolfie in London when in was 8 y/o! However, some of the later 'early' works were likely composed by others, including his father & Abel; 2) Sequence of these works - the numbers relative to the Symphonies was intermixed, but the Kochel numbers are in order; and 3) Performance - his first 'verified' symphony was written in 1764 and the last toward the end of his life a quater of century later - how should these works be performed? I like Mackerras' approach (why buy the box?), but of course there are so many other ways to perform these works. So, thus the questions - Dave 

Dave,
I have this box too, it is my favorite modern instrument set (by a good margin).
Interesting questions. Maybe ones that don't have a definitive answer either.
Authenticity - At this point, our best recourse on this question is the
Neue Mozart Ausgabe (The New Mozart catalog) which has finally been completed within the last couple of years. It is essentially the replacement for Köchel. The editor-in-chief of this project was Dr. Neal Zaslaw, who coincidentally authored a couple of superb books about Mozart, one which should be on everyone's shelf (
The Compleat Mozart), and another that is a specialist volume,
The Symphonies of Mozart. He also wrote
The Piano Concertos of Mozart, but since I don't have it, it remains lower in my estimation

. In any case, it is Zaslaw's contention that since we don't have the original manuscripts for a lot (most?) of these early works, we may never know for sure what the story is. So they are instead analyzed on stylistic grounds (a tricky proposition at best). The likelihood that they are by Abel is slim. There is little doubt that Leopold had a hand in some of them, at the very least in copying and correcting obvious errors. The creative part of them is most likely Mozart himself. You will note that the numbering jumps from #1 (K 16) to #4 (K 19). K 17 & 18 (#2 & 3) are omitted as being certainly not by Mozart. So there
are examples of works omitted. There are also works added, such as K 19a. This was a manuscript found much later on (in the 20th century, I believe) and attributed for mostly circumstantial reasons. Direct evidence is lacking in either direction. This is going to be the story on a lot of them, so you may never find satisfaction. I've decided to simply enjoy them, because whoever wrote them was a good craftsman.

The numbering is much the same. I don't remember the number of K 19a, but since it showed up after the "Jupiter" had gotten #41, it has a weirdly higher number, like #45 or something like that. Anyway, I almost never use the numbers so I don't care...

Performance - well, as you note, they span a relatively long period of time, one which was also chockfull of changes in performance. If you really want to hear something approaching the best we can do in recreating performance practice, I highly recommend dropping a fairly large chunk of change and getting the Academy of Ancient Music / Schröder/Hogwood set of 19 disks. A long time went into the preparation of this set. Zaslaw and Hogwood prepared all the scores and did a huge amount of research to make sure that each one was done as closely as possible to the original. I have no intention of getting into an argument with anyone on whether HIP recreates the past listener's experience, I'm just saying that they made a supreme effort to do as well as they could with it. The accompanying booklet (written by Zaslaw) is a trove of information too.

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Listening to:
Jiri Antonin Benda, 6 Sonatas and 6 Sonatinas, Fortepiano - Jacques Ogg - Sonata No. 5 in g minor, I Allegro moderato