It doesn't work that way. In order to get the route to load in TRS2019, you need to pass it through TS12 and or T:ANE first. Once converted, it'll load up fine. I did that with my TRS2004 route dated January 2004, going by the backup date and I was able to bring it in fine. I did laugh at my track laying an texturing though.
Bring in the route into one of the above mentioned versions.
create a slight change, like move a tree, or do something and undo it.
Save a new version to keep the old one.
Export the new one to a cdp and import that into TRS2019.
Once imported, check for missing dependencies and download as many of the missing ones you can if you have to.
The problem maybe assets that are missing if they're no longer available, and if they're not necessary, like a tree or something like that, they can be deleted using the delete missing assets.