Hi @Anonymous
Generally, Civil 3D incremental updates (.1 .2 .3 etc..) are rolled in to the next annual release of the software; so there is a very high chance that all the feature updates and sub assemblies in 2018.3 Update is available in the 2019 version. (especially the new Rail Subassemblies that were introduced at the time!)
Regarding Updates; I would like to clarify for the thread. The Autodesk Desktop App and the Online Autodesk Account do and will provide the software update available for the user only if the software is activated via a Serial Number or by logging to the application as a Named User (i.e. Single User-License).
Neither the Desktop App nor the Online Account will provide updates for software activated via a Network License (i.e. Multi-User License). The idea "from Autodesk point of view" is that if a company has an IT department to manage a Network Deployment then Updates should be handled by the IT department, the reason being is that the License Manager installed on the Server may need to be updated as well to accommodate newer software versions.
The IT Department, should definitely be able to log in to the Autodesk Contract Manager Online Account (the person who purchases the software) and download the updates in question and install them for the users, (some bigger companies push it through the Network for all users via a windows batch file!)
Side note, Network Licensing is going away eventually as Autodesk is in the midst of transitioning to the new Named Users accounts, so in time everyone will be able to install update a little easier.
Hope this helps,
Samir Rezk
Technical Support Specialist