Hi Aaron, When I uploaded my Sydney route to TRS2019 I did it via cdp files, and found there were initially about 350 assets that appeared to have missing dependencies.
However, I began with all train and train components, such as memeboy's NSW fleet. Most of the deps were easily downloaded except for two, which I looked up on TANE Content Manager. I then created a cdp for each, and then imported them into TRS19 and now all trains are okay. I did the same with davido and NSWGR_46class assets.
There were also a few payware items and a couple of JR assets, which I had to make individual cdp files from TANE, then import them into TRS19.
On a few occasions, I had a few 'open for editing' which I reverted.
Now no errors or missing assets.
Good luck mate,
Roy
PS: Also N3V was doing maintenance on the system for about 6 hours today, so this might have slowed things down.