Lets not overthink it. Whomever is holding the mags, owns the mags. All mags were purchased legally. Never consent to any searches.

Notarys don't care what a document says, they only verify that you are who you say you are as you sign the document. If the notary dated the letter (or their log) it would prove the date it was signed, but so would mailing it to yourself, or simply signing it and putting it away. Few if any will enforce this and unless a notarized document is mentioned in the law, it only hurts everyone else if some have it and some don't. Same for adding your own serial number to the mags.