If you’re still looking for unaccounted disk usage after doing a “Select all” then looking at those files’ properties and comparing that number against the space that Windows says you’re using, and after you’ve turned off Rescue and Recovery backups on your ThinkPad, consider looking in C:WindowsLogsCBS. In there, you’ll find logs used by Windows Installer module and by SFC.
On one of my clients’ computers, I couldn’t account for 26GBs (!) of disk space. Lenovo ThinkVantage Toolbox has a Drive Space Manager (look in System Health) which, when viewed by folder, showed me several very large files, around 10+GBs each, in C:WindowsLogsCBS.