Correct. I can and have installed 10d just fine, and I can install install 12.5 just fine, but I can't install 11d. It's important that I can take the upgrade path from 10d to 11d to 12.5 because I have a good amount of jobs to Copy from an older server, and as far as I know, jobs can't be copied between different versions of BE.
Also, even if I uninstall 10d, I can't install 11d. Again, no matter what, I can't install 11d.