My original submission on this topic was garbled, so I am redoing it.
The Notation Manual is clear that quoteDuring is a convenience feature:
It is very common for one voice to use the same notes as those from
another voice. For example,
first and second violins playing the same phrase during a particular
passage of the music. This
is done by letting one voice quote the other, without having to re-enter
the music all over again
for the second voice.
However, music so quoted is not sent to the midi file as demonstrated by
the following snippet:
\version "2.19.17"
music = \relative c'' { c,4 d e f }
\addQuote "music" \music
moreMusic = \relative c'' { r2 \quoteDuring "music" s2 }
\score { <<
\new Staff \music
\new Staff \moreMusic
>>
\layout { }
\midi { }
}
The pdf output (attached) correctly shows the two quoted notes in the
second staff. However, the midi file (also attached) has no notes in
channel 2, even though there is a channel 2.
This behavior greatly diminishes the convenience of using quoteDuring.
I think it's a bug.