Thanks. Nice and succinct summary.
My only reservation is the link you have posted for service centers . This link, however, is more for the purpose of locating service centers for physical visits, methinks.
This link I believe contains the correct addresses for the Lockboxs to mail applications to.
https://www.uscis.gov/i-821d-addresses
No doubt, they are then forwarded to specific service centers, in my case, Texas, probably based on work flows?