Your procedure to find the disklabel of the USB drive is perfect
You only seem not be aware of the following from
mount_ntfs
Code:
Limited support for writing
There is limited writing ability for files. Limitations:
o file must be non-resident
o file must not contain any holes (uninitialized areas)
o file can't be compressed
Note that it's not currently possible to create or remove files on NTFS
filesystems.
Warning: do not mount NTFS filesystems read-write. The write support is
not very useful and is not tested well. It's not safe to write to any
file on NTFS; you might damage the filesystem. Unless you want to debug
NTFS filesystem code, mount the NTFS filesystem read-only.