I'm in the process of renewing my passport and recently purchased some Special Delivery Guaranteed by 1pm envelopes. These envelopes come with a barcode for tracking purposes, but they also have a panel where you can affix stamps.

Here's where my question comes in, I have some 2nd class green stamps on hand, and I'm wondering if it's okay to use them on these Special Delivery envelopes?

I've noticed the instructions say "affix stamps to this panel," but I want to make sure that using 2nd class stamps won't cause any issues with the delivery or tracking of my passport renewal...

Has anyone here had experience with using 2nd class stamps on Special Delivery envelopes? Did everything go smoothly, or did you encounter any problems? Thanks!