Ah… the joy of using a Steinberg product with content provided. License and app installed fine. Steinberg library manager doesn’t see the content copied to the Backbone content folder (in Application Support/Steinberg/Content/Backbone) - no Backbone tab in the library manager as shown in the installation document. So what magic must be done, to register the content so the app can see it?
Ok-- figured it out and sharing for those who run into the same challenge. Take the 4 content files (3 from the download assistant and 1 from the install), select them all from the folder you copied them into, and then drag them over the Steinberg Library Manager app icon (not the open Library Manager app window). This will pop-up a dialog that allows one to determine how to register the content.
Thanks for sharing… Nice detective work… 
Curious though… are these content files the usual SB *.vstsound files.? If so, double-clicking these has proved a successful method of install previously…
For the future, will make note your method too though 
Indeed, double clicking a .vstsound file usually makes the Steinberg Library Manager register the file in its current location.
Good to know – thanks.
moving the library files over the app icon didn’t work for me.
I copied all the library files to the original backbone content folder, so I had all the 4 files in that folder (c:\programmdata\steinberg\content\backbone\vstsound) and opened the library manager again and voila: the backbone tab appeared. Then I checked the “move” box and selected my destination folder…