A Mozart puzzle...

If I don't practice one day, I know it. Two days, the critics know it. Three days, the public knows it.
JASCHA HEIFETZ
____________________________

In his book Mozart: A Life, Maynard Solomon gives the following description of Mozart's typical daily routine:

During his early years in Vienna, Mozart would customarily arise at six o'clock, be at his desk by seven, and compose until nine or ten, when he would make the rounds of his pupils, giving lessons until one o'clock.  "Then I lunch," he reported to his sister...  Returning to his room after several hours of social visits, he would again compose ... "I often go on writing until one - and am up again at six." ... With variations, that was Mozart's daily routine as he described it in his letters home... [On some] days the only time he had for composing was in the evenings, "and of that I can never be sure, as I am often asked to perform at concerts." (p.309).

With Mozart's time divided between composing, teaching, socializing, and frequent concert performances, the above description of his daily routine suggests that Mozart had no time to practice at all, or at least that he did not practice regularly enough to warrant mentioning practice among his daily activities.  This I find very hard to believe, but since I have no compelling evidence to the contrary, the best I can do is offer a few rather inclusive speculations on this matter.

1.  Solomon's description is incomplete and ignores evidence of regular practice.
If this is true, perhaps more knowledgeable readers will point me to the overlooked evidence.  (It is also possible that Solomon mentions practice elsewhere in his book and I simply missed it because I have read some chapters rather superficially.  There is, however, no entry for Mozart's 'practice' in the book's index.)

2.  Mozart's neuro-muscular endowment was so special that he did not need regular practice to give performances compatible with his reputation as a great pianist of his time.
This probably would make Mozart an outright miracle as an instrumentalist, and I don't believe in miracles.  All great concert pianists seem to have slaved at the keyboard to keep their neuro-muscular apparatus in top shape (and those who didn't - e.g., Schnabel, Cortot - payed for their neglect of practice with technically substandard or downright disastrous performances).  Horowitz, for example, liked to have people think that he never practiced, but in fact was witnessed (by the American pianist Leonid Hambro) to practice certain passages a hundred times or more in one sitting.  Rachmaninov - often mentioned as one of the greatest technicians in history - was reported (by the American pianist Abram Chasins) to have spent mind-numbing hours on practicing relatively simple pieces at one-third tempo. Mozart may not have needed regular practice to keep his own music in memory, but I doubt he could maintain the purely mechanical aspects of his piano playing in top condition without giving his fingers some kind of regular workouts.

3.  Mozart's piano music is simple enough to be played well by a skilled pianist without the benefit of regular practice.
I don't find this convincing because what makes a piece of piano music difficult to play depends in good part on the pianist's training.  Perhaps Mozart's music is simple for pianists who grew up on the Chopin etudes, but I doubt Mozart's training as an instrumentalist involved purely technical challenges appreciably beyond posed by his own compositions.  After all, Mozart himself thought that his two piano concertos from 1784 (K.450 and K.451) would "make the performer sweat"; and two centuries later these concertos were still described by the pianist and teacher David Dubal as "very tricky technically."
     It is also worth mentioning that Mozart's seemingly simple piano sonata K.576 is described in The Cambridge Mozart Encyclopedia as being "technically beyond all but the most experienced performer."  This description was seconded by the late pianist Charles Rosen who wrote that he had heard this sonata messed up in performances by such distinguished pianists as Walter Gieseking and Solomon.

4.  What Mozart played in concerts were simplified versions of the music that came down to us in the form of finished scores.
It is known that Mozart often performed the solo part of his piano concertos from memory because the solo part had not been fully written down in time for the concert.  Conceivably such partly improvised performances omitted technical challenges found in the finished scores, allowing Mozart to give polished performances despite lack of regular practice.  But then I don't know how this can be reconciled with Mozart's bragging that his concertos would "make the performer sweat."

5.  Mozart's public concerts contained enough wrong or missed notes, but in those days being considered a great pianist did not require giving note-perfect performances.
I do not know enough to evaluate the likelihood of this being true, except that Mozart's often expressed pride in his abilities as a musician does not seem compatible with technically sloppy performances.

This is about all I could think of on the question of why Solomon's description of a typical day in Mozart's life makes no mention of piano practice.  Which I'm sure isn't much since my knowledge of Mozart-related biographical and historical trivia is superficial at best.  Perhaps readers better acquainted with the seemingly endless list of Mozart-related books, monographs, and scholarly articles will be able to help me settle this issue.