With all the updates that appeared last night, I had several updates to 2021 versions. For example, my install of 15.4.1 (what I thought was the final) has shown no updates. Then, last night it shows an update. Looking at previous versions, it shows a 15.4.5, as well as updates to 15.4.2 and 15.4.3. None of the informational documents refer to those updates.
There are updates also for Media Encoder 1.4.5, Audition 14.4.3, After Effects 18.4.6, and Illustrator 25.4.5.
When security vulnerabilities are identifed in our apps or components that they use, we supply those fixes not only to the most current version of the apps, but also to the previous version. All of the minor dot releases you are referencing are security updates.