I searched this string on google:
site:lilypond.org/doc/v2.19 internals manual
And the first result is:
http://www.lilypond.org/doc/v2.19/Documentation/source/Documentation/learning/the-internals-reference-manual.nl.html
I think that files were accidentally copied to a wrong directory -
Documentation/source/ - (besides the regular one)?
http://www.lilypond.org/doc/v2.19/Documentation/source/Documentation/web/manuals
It shows the last version 2.19.21
Phil, it's a manual mistake than can be fixed or a problem in the
build scripts to be recorded on the tracker?