If you have a mailbox in the US, you need a notary to prove your identity. It's per mailbox, not per item. Bound items are, alas, not considered documents as you have discovered.
The US loves paperwork, they have forms for everything, and forms about forms (literally, there's a form you have to fill out when creating a form as part of the Paperwork Reduction Act, and trust me, anyone who says Americans don't do irony is lying). Even shipping across State borders is complicated. Weirdly, Americans don't trust anything that doesn't come with a significant form to fill in.