As the first phase of the communication subsystem / Matrix implementation was originally scheduled to land for Moodle 4.2, some of the files / versioning still follow that outdated information.

We need to check where any versioning / minimum version requirements etc (such as those in relevant version.php) are correct and up to date, and correct the relevant upgrade.txt file(s) to ensure they list 4.3 instead of 4.2, or remove them if they are not required since the communication subsystem doesn't exist until 4.3, so there's no "upgrading" happening yet.