On http://users.piuha.net/martti/comp/slackware/slackware.html , I read:

"It's good to have PKG_RCD_SCRIPTS and RCD_SCRIPTS_DIR settings in
/etc/mk.conf or otherwise the startup scripts are left in
/usr/pkg/share/examples/rc.d."

with the following code:

# Startup scripts for packages
PKG_RCD_SCRIPTS=YES
RCD_SCRIPTS_DIR=/usr/pkg/etc/rc.d

Shouldn't that last line read "RCD_SCRIPTS_DIR=/etc/rc.d" ?