It doesn't matter if you are running T:ANE or TRS2019 base-version. Both versions use the same installation process for DLC. Content Manager is still the same with some more improvements in '19 with some fonts being bigger, etc., and pick-lists management, but it's all the same otherwise. The only place where things differ is in TRS2019 Platinum and Plus with the Content Store for DLC, which is nothing more than a pretty interface for the same function of auto-downloading DLC. It's also unknown to us where you got your routes from since both are sold on Jointed Rail as well as by N3V through the content store.
With the third-party routes, you need to install everything in all the dependency CDPs regardless if the components exist in other routes. There are parts in these dependencies CDPs that do not exist in other routes along with stuff that might, and it's difficult to pull out what you need versus what you don't need. Trainz, any version, does not know what's in these packages so it will install all components.
The simplest way around this is to let the duplicate assets install. What will happen is since they are the same version, they will overwrite the current ones installed. Once the process of installing all the packages is complete, open up an Open for Edit view in Content Manager. Highlight all the open for edit assets, and choose Revert to Original. The assets are left open as a safeguard, but there's not much you can do other than revert them to original anyway. This is particularly true of built-in assets which can't be edited. Once you've completed installing Eagle River, use the same process with Coal Country if you got this one as well from Jointed Rail.
You will also be required to download any missing parts from the DLS as well. These are commonplace components that exist across all the routes and if you don't have them installed, they will be called for.
To download the ones you need, right-click on the routes and sessions that have missing dependencies. Choose download from the menu, and the parts will come in from the DLS. Anything that comes down from the DLS will not overwrite anything that's already installed because T:ANE knows that they already exist. This isn't the case with third-party asset packages.
Hope this helps.