Some of the more subtle things about the real boxes vs the electronics copies:

1. the electronics ones 'pinch' only a tiny sample of the real sound of a real box.

2. the electronics ones have a fixed phase of the constantly changing phase of the sound of a real one.

3. the electronic ones have a fixed relationship between the pitches of all the 'reeds', usually set up by direct 2 to 1 octaving - the real ones are often tuned (if they have been set up properly by a competent properly trained mechanic, not a self taught 'know all') in very subtle pitch differences from the theoretical 'correct' pitches, thus the sound is different.

4. the real ones generate a 'chorus effect' - a real 'stereophonic' sound, because of the phase differences between reeds of the 'same' (see 3 above) pitch moving together and apart, as well as the fact that the pitches are nudged lower in the bottom half of the keyboard and higher in the treble. Also, there is a tiny pitch difference between the difference between the various 'octave banks' of reeds in the real boxes - if they haven't been ruined by ignoramuses with 'tuning meters'. Also, like a pipe organ or a choir, the pitches of each reed can subtly drift, causing more delicate phase differences.

5) when 'pulsing' the bellows, and vamping the buttons/keys, you can affect the sound in ways that the electronic ones cannot normally emulate - volume differences between the two sides (most people - including players - are stunned to see this effect!) and pitch differences caused by a non constant volume of air thru the reeds. However, different real boxes are more or less sensitive to some of these 'bellows effects' - one of the reasons why I have more than one instrument. A reed vibrating constantly gives a louder perceived pitch than one that is being pulsed - thus this side sounds louder.