I only had a covered (full case) ammo box once, when the retailer needed to ship it by Canada Post for whatever reason haha.
TDG also states you need to have an identifying label on Dangerous Goods. International TDG states packing provisions for ammunition are P130 and LP101
https://adrbook.com/en/2017/Sutun/8/P130
It does not say to cover the outer box to prevent identification under provision P130. Regardless, if you're in the shipping business you know what is in there as well as covered rifle boxes. The mail man knows who smokes Justin's marijuana and who buys adult toys.