Context
My current "instance" of Qt has existed since July 2015. Through this instance, I've previously installed and then uninstalled Qt 5.5, Qt 5.7, and 5.8.

Issues
Even though I uninstalled Qt 5.5, 5.7, and 5.8, all their documentation and examples were left behind.

Furthermore, because I had installed Qt 5.7.0 but not 5.7.1, the "Update components" option in MaintenanceTool.exe still prompts me to update the Qt 5.7 docs/examples (even though I have no 5.7 binaries anymore)
 

Workaround
From http://lists.qt-project.org/pipermail/interest/2017-June/027381.html : Launch MaintenanceTool with the --show-virtual-components argument and manually uninstall the documentation/examples