... rather disks that are "reserved" by USBMSD.ADD.
If you tell USBMSD.ADD to prepare 8 units via setting the
/REMOVABLES:8 switch then USBMSD.ADD will report to the OS
that it is managing 8 units even if no USB stick/disk is plugged in.
That's because of a limitation in OS/2 that needs to know
already at boot up time how many partitionable devices are there.
You can easily test: change /REMOVABLES: to another value and see what
DosPhysicalDisk will report back.