HI Karl-WE - I reached out to the product team. Here is their reposnse:
This is by design. Moving from 1903 to 1909 is done through an enablement package to light up features within the same “line” of Windows 10, such that 1903 and 1909 are actually the same code base completely. To this end, they receive EXACTLY THE SAME monthly updates (LCU’s) which will have the same package number.
HOWEVER, the enablement package is used to “trick” the naming convention that is seen such that one will show the name as 1903 and one will show the name as 1909. If you dig into the database for the package numbers, however – they will be the same because they ARE the same.
This should reinforce to all of our enterprise customers that the “upgrade” from 1903 to 1909 is not actually a code change as it is technically the same line of Windows 10, and should NOT be viewed as a version change.
Hope this helps...