Do I need the creator's approval to add their creations to my shelf?

No. If you have the physical copies on hand, open "Add creations to the shelf" under your stocked creations, search by creator or creation name, and add them to the shelf right away. When you do, a note saying the creation was added to your stocked creations is written in your Contact Note with that creator, and the creator is told by email. If you add several creations on the same day, only the first notice is sent right away; the rest arrive together the next morning. If a creation turns out to be one the creator does not recognize, they can remove your place from its handling places, and you will be told when that happens. To approach a creator you have not worked with yet, use "Contact" as before.