You're confusing the command again
-L, --listfiles package-name...
List files installed to your system from package-name.
-S, --search filename-search-pattern...
Search for a filename from installed packages.
dpkg -S /my/file/path
Finds which, installed, package installed the file.
dpkg -L samba | grep .conf
Greps through the list of files installed by a given package.
If the file you want isn't in there then it wasn't installed by the package itself (could be created on the fly by the binary for example), in which case obviously the package system can't track it.