Discussion on how to prevent users picking an out-of-date mirror

When I am developing apt-smart, an automated Debian/Ubuntu mirror selection tool, I found that some Ubuntu mirrors listed in the official mirror_list (link1, link2) are seriously out-of-date via Travis CI test logs. For example, in a log several days ago:

| 79 | http://mirror.atlantic.net/ubuntu | Yes | No | 6 weeks behind | 416.7 KB/s |

in another log a month ago:

| 80 | http://mirrors.arpnetworks.com/Ubuntu | Yes | No | 20 weeks behind | 425.78 KB/s |

(apt-smart downloads the Release file of a mirror to benchmark download speed and parse Date value in the Release file to detect the mirror’s last update date)

Why outdated mirrors are listed in the official mirror_list (link1, link2) , and the mirror statuses shown on page of link2 are inaccurate or just lack (Last update unknown)? What is the method the backend using to detect whether a mirror is outdated?

What’s worse, Ubuntu’s Software & Updates(a.k.a software-properties) takes no steps to prevent users picking an outdated mirror, even when the user clicking Select Best Server. Google search result shows that users complained the issue. There is even a reported 6-years-old bug titled Software-properties mirror selection may pick an out-of-date mirror, but without any fix.

What should we do to prevent users picking an out-of-date mirror, on mirror_list server side and Ubuntu end user side?

I am not sure I post to the right place, correct me if I am wrong please. Thanks!