https://github.com/joomla/joomla-cms/blob/4.0-dev/administrator/components/com_admin/sql/updates/mysql/4.0.0-2016-19-03.sql The update file is present. Does anyone have any thoughts here?

This file is not executed (as explained many times now) if you are on 4.0.0-whatever you need a file starting with 4.0.1 that it is called. Else we asume this file is already loaded asyou are technical already on 4.0.0. So this file is only triggert if you are on a version lower than 4.0.0 or the file is targeted for 4.0.1 ;)

closing as expected Behaviour (not in my Eyes cause Update is easier than fresh Install).

The version part of that string shouldn't matter since we're using dated diffs. We need a system that can work independent of version numbering so it ultimately becomes clear that when performing an install or update that there has been a change that needs to be applied.

Reopening. This is an item that needs attention. Period. This and #13661

Then can we create a specific item that targets the real issue that the version file is not recognised rather than the this specific namespace issue

All it takes is updating the issue title/description. I wouldn't change much in the description though because then it changes the context of the follow-up discussion thus far.