Windows 10 is different than previous versions of Windows. Previously Microsoft came out with a new number (sometimes a sequential number like 3 or 7 or 8 and sometimes a number representing the year released like 95 or 98 for 195 and 1998 or in the case of ME and XP picked letters).
When Windows 10 came out they said Windows would no longer be an operating system you got new versions of Windows, but would be a service that continuously updated. This is quite often referred to as WaaS or Windows as a Service, similar to how many programs work now that are called as SaaS or Software as a Service. You would always have the latest version was the idea.
They went to a plan of offering the updates twice a year in September and March although that has not worked as well as planned.
You will see talk of versions 1803, 1809, and now 1903 and 1909. These numbers are not build numbers as you would see in the past where as they developed the software they kept adding numbers so the developers knew what they were using and then one of them was deemed worthy and released and everyone knew changes that had been made.
With these new numbers the first two numbers are the year of this release and the second two numbers show the year they planned to release. 1803 means it was released in 2018 and was planned to be released in March although they were about one month behind.
The 1809 release got interesting. It was released in October 2018 and then quickly people started reporting it deleted their data and Microsoft pulled the release and made repairs and then release late November. Another set of major problems appeared and Microsoft pulled again, which raised questions about their quality testing. They released in January and buy then every one was leery of it and smaller problems appeared and it went through more revisions but is out there. 1903 was to arrive in March originally however is just now arriving in late April / early May. Most organizations chose to skip 1809 and now will move on to 1903.
Hopefully Microsoft has everything stabilized again in the fall when 1909 should arrive in September 2019, but more likely October, however still with 09 as month. Donít teach your children the month numbers using the Microsoft calendar. It confuses us adults also.