precisley Willum, by Jove you've got it!
in the same way that a missing preset style from previous model will be replaced by the closest equivalent, a missing sample will be replaced by an equivalent. Thus it is a hit and miss affair. If you just record a piano you "may" not notice a great deal of difference in playback of a recording. If you specialist edit sounds tailored for each song, particularly using them in composer and pads with defined internal pitch points and chord modify changes designed for the progressions in the song as I do, you will notice far more problems with replaced samples.
The silence is when there is no equivalent sample built in.
The soprano only works for 2 octaves... the natural vocal range. Either side is other samples, the top one from a built in sample with vibrato added in the edit, not recorded in the sample. Thus this octave is the same with the card removed. Many sounds are "padded" out with sounds not necessarily produced naturally to prevent silent keys beyond the natural lower and upper range of the voice.
As for the Jazz Guitar Mute, this is just the same point I made in the experiment in my previous post. However this needs to be done in sound memory for accurate results, this exactly reproduces the effect of the removal of the card while still having the card in place, panel memory will just produce extra variables. Even though the entire mapping of tone, amplitude, pitch, filter, LFOs and effects are identical, the primary arbiter of timbre is the base sample. Change that, and you've effectively changed the recording to that of a new instrument.
The "nasty noises" are programmed modulation effects. For M&F Choir Ooh, M&F Choir Aah, Heavenly Voices and Softly Speaking they are easily removed in filter envelope by flattening decay 1 to 100 for all active samples.
best regards