Joe_Lurie thanks for taking your time to ask and reply.
I know the details, yet it doesn't seem to be impossible to fix.
There is a paid script from AJtek WSUS automated maintenance that is able to fetch the build number in the WSUS DB and correct the version string of Servers and Clients incl. 1903 and 1909.
So please forgive me if I am not believing that it is by design, when it can be changed at any time.
Since it's now official we will see same great technology achievement happen again in 20H1/20H2 I can just plea that the WSUS team has a look what Adam has accomplished.
https://www.ajtek.ca/
I don't expect the team to make the whole script obsolete, yet version strings would be a great beginning. They should try it out and review the code how it is done.