This is for the people that did not get their copy of AP upon entry or didn’t get it stamped.
I suggest to please make sure you get it stamped, if the officer does not, kindly ask them to please stamp it and give you the second paper for your records. However, if that is not possible do not worry, you have your passport stamp (if you do not get this stamped make sure to please ask them to stamp it for evidence), which is proof of your entrance.
You must at least get one of the documents sealed, either the passport or the Advance Parole BUT make sure you get your passport, both documents will be ideal but sometimes the officers do not do it.
If this happened to you, you may check your official entrance with Parole online for further evidence and for your records it is called the I-94:
It might not appear right away so be patient, and keep checking!