From the manual, 10.3.1,
http://www.lilypond.org/doc/v2.7/Documentation/user/lilypond/Creating-
titles.html
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As demonstrated before, you can use multiple \header blocks. When
same fields appear in different blocks, the latter is used. Here is a
short example.
\header {
composer = "Composer"
}
\header {
title = "Title"
}
\score {
\new Staff { c'4 }
\header {
title = "New title" % overwrite previous one
}
}
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However, this example does _not_ overwrite the previous definition of
title with "New title". (at least, not in 2.7.38) Is this
intentional or a bug?