The upgrade would likely not interfere with the activation process, however, you can always save the licencing info just in case.
The errors weren't there because everything is very complex in the registry, when you fix one key, there are other items that are detected, both within other areas of the registry and the filesystem. The errors were not caused by the "premature" installation as you call it. If there was an error preventing the install, the install wouldn't go through. Your conclusion is also incorrect, there are updates that can be installed. It all depends on the type and the severity of the error. After the upgrade, Disk Cleanup can be performed and all the remnants of Win7 removed. A rollback would definitely not be advisable. Neither do I, but I don't want to keep you waiting for a long time, because you have been waiting for an extraordinary amount of time and deserve a solution, so I inquired about Win10 as this would likely be quicker for you, but I see no issues with fixing Win7 other that it's going to take a lot of time. :)