I cannot verify if this step is necessary since I had installed that upgrade. It doesn't seem to be necessary any more - I had only launced one of the programs.) (This step was suggested by the instructions based on the 2014 article. If you lack these (either because you deleted them or never had them installed first hand) and never registered the purchase with your Apple ID, you need to work your way up through the missing years of upgrading, including the registration with your Apple ID to be offered an installation on any system that's older than the currently shipped Mojave:
You need to have an old version of Pages, Keynote and Numbers installed in your Applications folder to be able to update them.
