After LTS upgrade to 20.04 mdadm init.d are all broken links

[A]

Upgraded a number of servers (more than 30) from various LTS versions to LTS 20.04
In each case that uses mdadm, all links for mdadm in /etc/rcX.d/*mdadm* are broken links.

Every upgraded server using mdadm matches the issue exactly, but choosing one server:
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.2 LTS"

mdadm:
  Installed: 4.1-5ubuntu1.2

Easiest way to see the issue is to type:

# ls -lasd `find /etc | grep mdadm`
4 -rw-r--r-- 1 root root 831 Dec 15 22:36 /etc/default/mdadm
4 -rw-r--r-- 1 root root 3426 Feb 28 2014 /etc/logcheck/ignore.d.server/mdadm
4 -rw-r--r-- 1 root root 411 Feb 28 2014 /etc/logcheck/violations.d/mdadm
4 drwxr-xr-x 2 root root 4096 Dec 15 22:36 /etc/mdadm
4 -rw-r--r-- 1 root root 982 Dec 15 22:36 /etc/mdadm/mdadm.conf
4 -rw-r--r-- 1 root root 379 Jan 15 2020 /etc/modprobe.d/mdadm.conf
0 lrwxrwxrwx 1 root root 15 Jul 3 2016 /etc/rc0.d/K01mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 24 Dec 15 22:11 /etc/rc0.d/K05mdadm-waitidle -> ../init.d/mdadm-waitidle
0 lrwxrwxrwx 1 root root 15 Jul 3 2016 /etc/rc1.d/K01mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 15 Dec 15 22:09 /etc/rc2.d/S03mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 15 Dec 15 22:09 /etc/rc3.d/S03mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 15 Dec 15 22:09 /etc/rc4.d/S03mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 15 Dec 15 22:09 /etc/rc5.d/S03mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 15 Jul 3 2016 /etc/rc6.d/K01mdadm -> ../init.d/mdadm
0 lrwxrwxrwx 1 root root 24 Dec 15 22:11 /etc/rc6.d/K05mdadm-waitidle -> ../init.d/mdadm-waitidle

Since init.d/mdadm and init.d/mdadm-waitidle don't exist, all the /etc/rcX.d/*mdadm* links are broken links
- and in a colour terminal are all highlighted distinctly

All systems boot successfully, so I'm not sure if it is simply a cleanup issue during upgrade from 18.04 to 20.04, or if the files should exist?

However, a previous version desktop, which is:
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.2 LTS"

has init.d/mdadm and init.d/mdadm-waitidle thus they aren't broken links