Might just add a note that is advertised for the TRS 2019 product on the Trainz Portal site:
MORE THAN JUST DRIVING TRAINS
Trainz Railroad Simulator 2019 is the most expandable, customisable, extendable train simulator ever created.
"EDIT BUILT-IN ROUTES
In TRS19, you can edit and update all the built-in and "DLC" (payware) routes and sessions. Share your edits with other content owners via the Trainz Download Station".
So anything on the DLS that is freeware may be downloaded by registered users that can be used to make layouts and sessions.
Some 3rd party asset designers allow re-skinning provided that they are only used (hosted) on the Trainz Download Station.
Also many members like to customize dependencies in order to make them function correctly with handy tools like the AssetX program.
It is all about team work using the efforts of non-profit content creators sharing their talented work together.
So when it comes to copyright where is the line drawn?