don't need to do the base game if there's a patch, but you need to use the base game to build the backported patch pkg. it's required, so it's best to keep all pkgs you download on an hdd as backup, because you might need the base pkg. if you have to repackage the patch, like if it came from a different source, the base game will be needed to do so as well.
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this is not needed all that often though, because most people are using the same dumps of the game. however, if you were to use those backport apps, you'd need the base pkg that's installed on your system or it will error upon installation, if it's a different dump, the patch that is.