How to pull a different version of the package (deb) from the repository?

Question

Debian

The question originated on raspbian, but I think it applies to all-debian and apt.
In the repository directories, I see two versions of the package.
raspbian.raspberrypi.org/raspbian/pool/main/p/prom...
[ ] prometheus_1.5.2+ds-2_armhf.deb 21-Feb-2017 10:08 4.3M Details
[ ] prometheus_2.7.1+ds-3_armhf. deb 21-Feb-2019 10:08 9.2M Details
but, apt get, search, versions the second (2.7.1) stubbornly doesn't show me.
apt install prometheus=2.7.1
Reading package lists... Done
Building dependency tree
Reading status information... Done
E: Version '2.7.1' of 'prometheus' not found
Where are these things even regulated?

Answer 1

If a package is not searched with apt search, then it is not in the list of packages. The package list is at raspbian.raspberrypi.org/raspbian/dists/stable/mai... (for stable main)