Possible solution
Hi Robe Rider.
I had the same problem in TS2010; clam1952 told me how to fix it.
Log into Planet Auran or the DLC, look up your order history. Open the page for the T1 pack. In it you will find the serial number for your T1 pack. Copy that (I popped open the txt file where I saved my TS2010 serial number and pasted the T1 serial number into it, after which I backed up that txt file for safekeeping).
Then I logged out of Planet Auran and opened Trainz. On the first screen (the "Launcher") click on the "Options" button. On the first tab, "General", enter the Serial Number for the T1 pack and click the "Add" button. When it appears in the big list box under your other Serial Numbers, click "OK" and then click the "Quit" button on the Launcher screen. You will get a popup about searched for deleted assets, new assets, etc. I just let that do its thing and waited until it closed out Trainz completely.
After that, everything for the T1 pack showed up!
Many thanks to clam 1952 to telling me how to fix this!