It is very likely that there will be additional chords, arpeggios, and all kinds of difficult passage work integrated to upscale the piano score. This will be done according to the characteristics of the historically varying taste of the arrangement, burdening the pianist with an additional layer of stylistic interpretation, on top of the originally conceived composition.
In the hands of Lucille Chung this does not seem to be any problem whatsoever. With her usual élan, she delivered the most zealous performance, in which she, seemingly effortless, handled the most vociferously difficult passages in a musically always convincing way.
Particularly in the case of transcriptions, it certainly depends very much on the presentation of the performer to bring out all the specific characteristics demanded of the "new version" of a piece.
Lucille Chung commented on this process in La Scena Musicale, on the occasion of the release of her CD by XXI Records: "The challenges of playing transcriptions lay in the credibility of the orchestra and the piano part as one, and in preserving the right colors and nuances."
And she continues:"… also the timing [is essential]. An orchestra is much more ample, vast and takes more sound - so the timing is different from just playing solo parts. I studied the core and the instrumentation to know what should come out each time. It's important to get the same character as the orchestral piece, to sound like strings here or timpani there, to also make it sound more like a dialogue."
Transcriptions seem to be meeting a new and popular demand. At the famed Verbier Festival last summer (2009), Lucille Chung and Alessio Bax, who are also married to each other and perform together often, took part in an interesting cooperative performance with Emanuel Ax, as well as pianists J. Quentin, S. Trpceski, N. Goerner and J. Wang. Besides various arrangements for four and six hands piano, like Strauss' "Radetsky March" and "Trisch-Trash Polka" for six hands, they performed a transcription by M. Wilberg of "Carmen Suite" for four pianos, and Vivaldi's "Four Seasons" for four pianos. The transcription was by N. Economou, and although I was not able to hear that presentation, I was told that it was most memorable for its elaborate production and the cooperation between the participating pianists who took turns performing.