Why does the Security Update in Mac OS X get reinstalled?

Question

macOS

This is not the first time I notice that Makosi security updates are installed twice.

They upload their gigabytes, require a restart, install for a long time, restart again - and ... again they write in the updates that there is one “new” that will require a reboot - exactly the same as what has already been installed! Just now or a few days ago. Again, downloading gigabytes, restarting, installing.

High Sierra 10.13.6, but the situation was the same on other versions.

The same system update is installed a second time.

screenshots

I have 2 drives: an old hard drive with an old system and a new SSD with a new, working system. Perhaps having two systems is associated with such painful updates? If you just delete the folder on the old hard drive (which one?) - will this get rid of duplicate updates?