root@x3:~# ( cd /var/lib/apt/lists.save/ && for i in *_Packages; do echo ${i/.ubuntu.com_ubuntu_dists/}; done ) | sort 
archive_xenial-updates_main_binary-amd64_Packages
archive_xenial-updates_restricted_binary-amd64_Packages
archive_xenial_main_binary-amd64_Packages
archive_xenial_restricted_binary-amd64_Packages
security_xenial-security_main_binary-amd64_Packages
security_xenial-security_restricted_binary-amd64_Packages