> Because we only try VOLUME_NAME_DOS, this function always fails for a volume that's not mounted as either a drive letter or a junction mount point.

If a volume is not mounted, users have to use \\?\ or \\.\ either directly or indirectly via a symlink or a junction to get to it, right? Do you think such uses are common enough to warrant dealing with VOLUME_NAME_GUID? Also note that pathlib currently expects DOS paths only: it will strip '\\?\' prefix in resolve(), making GUID path "invalid" (and, also, precluding direct usage of '\\?\' prefix with resolve() in other cases unless users are not prepared to deal with it).