From Section "E" of the linked info:
"any package or other container in which there is any firearm or ammunition without written notice to the carrier".
Here is the entire text of section "E". Read the entire section. I will highlight the relevant part:
(e) It shall be unlawful for any person knowingly to deliver or cause to be delivered to any common or contract carrier for transportation or shipment in interstate or foreign commerce, to persons other than licensed importers, licensed manufacturers, licensed dealers, or licensed collectors, any package or other container in which there is any firearm or ammunition without written notice to the carrier that such firearm or ammunition is being transported or shipped;
except that any passenger who owns or legally possesses a firearm or ammunition being transported aboard any common or contract carrier for movement with the passenger in interstate or foreign commerce may deliver said firearm or ammunition into the custody of the pilot, captain, conductor or operator of such common or contract carrier for the duration of the trip without violating any of the provisions of this chapter. No common or contract carrier shall require or cause any label, tag, or other written notice to be placed on the outside of any package, luggage, or other container that such package, luggage, or other container contains a firearm.
If I'm sending a gun back to the manufacturer for warranty work, how is it a violation? As that code is written, I'm under no legal obligation to diclose if it is a firearm if sending it to the manufacturer.
Also, please send me the link for your reference ("ATF SHIPPING LAW"). I didn't know that "ATF SHIPPING LAW" superseded US federal law. I linked to US Code. That is the law, period. Not some FAQ page from the ATF website. The ATF doesn't write laws, and their FAQ page wouldn't stand up in court.
I found an old thread on this site where the same thing was being discussed. Here's the link. The hang up there mirrors the one in this thread.
As far as your second point about the gun being lost or stolen, fair enough, but I want to focus on Federal law.