Incorrect file(INSTALL) documentation or implementation deficit?
Currently the file(INSTALL) documentation states:
The INSTALL signature differs slightly from COPY: it prints status messages (subject to the CMAKE_INSTALL_MESSAGE variable)
I don't think the status messages are subject to CMAKE_INSTALL_MESSAGE currently.
CMAKE_INSTALL_MESSAGE only influences how install() might generate file(INSTALL) commands (using undocumented flags like MESSAGE_NEVER).