Adding a data point that corroborates this report (package downloads via apt, not just Release/Packages metadata).
Since today (2026-09-07), `apt-get install` on Debian 11 (bullseye) fails with 404 errors for several bullseye-security packages when fetched via deb.debian.org 404 http://deb.debian.org/debian-security/pool/updates/main/v/vim/vim_8.2.2434-3+deb11u3_amd64.deb 404 http://deb.debian.org/debian-security/pool/updates/main/g/gnupg2/gnupg_2.2.27-2+deb11u3_all.deb 404 http://deb.debian.org/debian-security/pool/updates/main/g/glibc/libc-dev-bin_2.31-13+deb11u14_amd64.deb
