Stephan,
I can't speak directly about your post. But when all this new LR flavors came out, and seeing the concerns mentioned here on LuLa, I thought I should get LR6 on this newer machine, just incase. I had the boxed DVD and license key, whet through the download process, updated to 6.14.
I could not find LR6 in my Application Folder on my Mac. What I thought was LR6 would open the new flavor. I had many duplicates of .lrcat-2. Was kind of a mess. After careful thought and inspections, I deleted many catalogues, 6 or more. Some of this may have come from updating to the new Classic. My few catalogues are OK though.
So I gave up on trying to get LR6. Don't want to go through that again. Am very happy with the CC Classic.
Hope someone here has a solution for you.