Computerworld - https://www.computerworld.com/article/3269292/microsoft-windows/why-microsoft-gave-windows-10-version-1803-a-different-name.html#tk.rss_all
Microsoft will start distributing the next Windows 10 feature upgrade, “Windows 10 April 2018 Update,” today – a few weeks later then it had been expected to arrive.
The release date barely squeaked under the wire Microsoft set for itself with its labeling of the upgrade, although the company has never expressed concern when actual release dates have conflicted with each update’s alternate – and numeric – title, the one formatted as yymm. That conflict continued with the April 2018 upgrade. Its 1803 moniker envisioned a March, not a last-day-of-April, debut.
[ Further reading: Windows 10 April 2018 update: Key enterprise features